[BrianG]

For shimming, you want to shim the pinion have no slop right before the point where you get binding.

Not sure what the PSU specs for the 360 are, but look at the 12v rail (may have several supplies). Usually, they rate TOTAL power, not just on one rail. Look at the current rating for each rail. As far as a loading resistor, it depends on the design. Usually, around 1A loading is fine, but takes experimenting to find out which supply rail is used for the regulation. Normal computer supplies usually need the 5v or 3.3v loaded if any. For the 12v rail, use something around 10-12ohms and 20w. For 5v, use 4-5ohm and 10w. For 3.3v use 3-4 ohm and 10w.