Originally Posted by ToraKitsu

Well, the differences are that the front one-way drives both front wheels independently, meaning they drive at different rates, regardless of whether the car turns left or right. Remember....during turning, the inside wheel turns at a slower rate than the outside wheel. The front one way compensates for this difference, and still drives both wheels, whereas a differential drives only one, at any one time. A locked front diff spins both front wheels equally, which also doesn't make up for the difference in wheelspin in turns.
In a 50/50 drifter, it makes no difference, but since CS overdrives the rear wheels, this difference is magnified because the wheels are turned in the direction of the drift.
Having two one ways on the same end complicates things only mechanically. The extra one way is a redundancy, meaning there is no purpose for it to be there, but it doesn't hurt performance any. If you have a front one-way and a center one way pulley, the extra one way does not add to performance, just mechanical complexity.

And I wouldn't get stuck on trying to find aluminum equivalents for all the pulleys. It sometimes isn't possible. I have 50/50 and CS chassis that have pulleys made of different materials on the same chassis. As long as they do their intended purpose, it doesn't matter what they're made of. Once the body is mounted, no one can see them, anyway.
CS kits address the pulleys required to change the ratio of whatever model they are made for, so if you are having trouble finding an aluminum pulley, it's probably a good bet that it isn't a required pulley that needs changing. Still, another source to try is Eagle Racing. They make CS kits for almost everything belt driven out there.