I have the GW1 rules so here it is in that format:
Centisteed
# appearing 1
AC 9 (which for a PC would be shield only)
Movement 30
Hit Dice 7 (d6)
This long-bodied mammal was once a horse, but the mutations it has undergone have given it an almost insect-like appearance. A centisteed can trot at full speed on its 16 legs carrying two human-sized riders. Although not intelligent by human standards, the centisteed is totally immune to all forms of mental attack and possesses force field generation. While they make desirable mounts, these beasts also require enormous quantities of fodder because of their increased metabolism. In a combat situation, the centisteed is almost more trouble than it is worth, as one of its riders must devote all of his efforts towards keeping the centisteed under control.
Force Field Generation: This endows the mutant with the power to create an invisible wall of energy through which physical objects may not pass. The wall forms around the body of the mutant (about 15 centimeters out) and will take 5 dice of accumulated damage (as though it were the mutant) before being forced down. The force field requires no effort to maintain once it is established and will last up to one hour (unless it is driven down by damage) before it dissipates. Only one such force field may be generated by the mutant in a 24 hour period.
Increased Metabolism: This defect forces the mutant to spend great amounts of time feeding. it must carry large quantities of food when traveling, and in combat, must stop every 5th melee turn and spend one turn eating, before returning to battle, or lose 1 point of physical strength and 2 hit points each melee turn thereafter. NOTE: these losses are temporary 
*A melee turn equals 10 seconds. 

Okay I want to salvage this critter:
In general fan material on the web several changes have been made, first this creature has been suggested as a herd animal, so can be found in small herds... large herds would probably be bad for the environment, which is probably why it says 1 in the original material (that and the game designers probably wanted to make it hard for PCs to acquire). Also there is of course debate as to wether or not this is a natural mutation because of Gamma World environment or an escaped GMO developed for racing before civilization collapsed. Also there seems to be a tendency to imagine this animal as a trotter or pacer or ambler in gate.

I converted speed as follows:
1 GW1 melee turn = 10 seconds. The movement rules for creatures indicates the speed per turn in meters is average normal speed (walking along), and then you multiply by 5 to find the maximum speed. So a GW1 creature of 30 can move a maximum of 150 meters ever 10 seconds. Multiply this by 6 melees equals 900 meters a minute, multiply by 60 would give a speed of 54,000 meters per hour or 54 km per hour maximum. 30 x 6 = 180 meters per minute x 60 = 10,800 meters per hour or 10.8 km per hour for normal movement. In SF the turn is 6 seconds so that is 10 turns to equal 1 minute. 180 meters divided by 10 would equal 18 meters normal gait per turn or 90 meters per turn top speed. 
I like my Centisteeds to look a bit more insect/horse fusion than just horses with a lot of legs. When comparing Gamma World, SF Alpha Dawn & SF Gamma Dawn there are some differences… SFGD states: 

Force Field Generation 
Mental; Activated, SL
The mutant is able to create an invisible barrier of force around himself that protects him from physical danger. This includes energy attacks and radiation.The force field forms a smooth surface about half a meter from the mutant's skin.
The GW1 Centisteed only generates a 15 centimeter field versus 50 centimeter field, but 1/2 a meter is a good range and seems reasonable.
The character cannot make physical attacks while the force field is up, but can use mental powers.
There is no indication in GW1 that it can not make physical attacks or engage in physical activity.
The force field absorbs 5xSL points of damage. It renews itself at a rate of 5 + SL points per round. It can be kept up 5 + SL rounds. After that, the character must drop the force field for an hour before using it again.
In GW1 it appears to be a total of 5d6 or 30 points of damage, which would mean the Centisteed would be equal to SL 6 or SL 5. If I go with the SFGA rules as a guide that means it renews the field at the rate of 5 + 6 SL = 11 points per turn, and it can be kept up for 11 rounds (turns) as well for a total of 66 minutes. Or if using the lower number 10 points per turn, and 1 hour.
If the force field takes enough points physical damage to destroy it, the character must make a STA check or fall unconscious. Any excess damage is applied to the character. If the character falls unconscious due to a mental attack or some special circumstance, the force field shuts off at the end of the round.
My understanding is combat round and turn in SF are interchangeable terms.

So here is what I am suggesting for SF. Input is most welcome.

Background: If this is a general setting it could be a domestic GMO or if your space includes a colony/planet that got heavily nuked say by the Sathar... maybe this critter just appeared, and with the planet being reclaimed it has been discovered and has become a creature that can be encountered in the wilds of said planet, perhaps Centisteeds have even become a popular racing animal, or future rodeo animal that is now exported from said world to the rest of the UPF. Some fan sites suggest that wild Centisteeds can actually through a rider with their force field alone, and require specialized tack and saddles to ride... no bareback riding these ponies.

Suggested SF Stats: Centisteed:
Type: Large Herbivore
Number: 1-5 in the wild, can be kept in larger herds in domestic settings.
Move: Fast: (Paces 90 m/t, Fast Ambles 30 m/t, and normal ambles/walks 18 m/t)
IM/RS: 7/65
Stamina: 200
Attack: 55
Special Defense: Force Field Generation
Special Attack: n/a
Damage: 4d10 (all those hooves)
This long-bodied mammal was once a horse, but the mutations and or genetic modifications it has undergone have given it an almost insect-like appearance. The Centisteed has tougher hide that is more of an exoskeleton like hide than what occurs on normal equines and they posses compact eyes. This hide can be very beautiful, striped, spotted, brightly marked and even posses iridescent qualities. A Centisteed can pace at full speed on its 16 legs carrying two human-sized riders, at slower speeds the animal has various gaited or ambling gaits that give an incredibly smooth ride. Although not intelligent by human standards, the Centisteed is totally immune to all forms of mental attack and possesses force field generation. While they make desirable mounts, these beasts also require enormous quantities of fodder because of their increased metabolism. In a combat situation, the natural Centisteed is almost more trouble than it is worth, in combat one of its riders must devote all of his efforts towards keeping the Centisteed under control. The only exceptions to this would be very rare Combat Modified Centisteeds, such beasts would probably have implants or be part of further genetic modification breeding experiments by governments or corporations working on improving the wild Centisteed type for military use. A natural Centisteed attacks with it's hooves but will usually choose to flee if it has that option.
Force Field Generation SL5: This endows the Centisteed with the power to create an invisible wall of energy through which physical objects may not pass. The wall forms around the body of the mutant (about 50 centimeters out) and will take 30 points of accumulated damage before being forced down. The force field requires no effort to maintain once it is established and will last up to one hour (unless it is driven down by damage) before it dissipates. In combat the field renews at the rate of 5 + 5 SL per round. Only one such force field may be generated by the Centisteed in a 20 hour period. If the force field takes enough points of physical damage to destroy it, the Centisteed must make a STA check or fall unconscious. Any excess damage is applied to the Centisteed.
Increased Metabolism: This defect forces the Centisteed to spend great amounts of time feeding. In combat it must stop every 8 turns and spend one turn eating, before returning to battle, or lose 1 point of strength and 2 stamina points each melee turn thereafter. NOTE: these losses are temporary.