I've always used brass since it won't hurt anything steel. But you do need to be aware to check both ends of your drift now and then to make sure you haven't mauled it enough to cause chips to flake off. Gentle handling is all that you need and that shouldn't cause issues but if you do enough wheel disassembly and then reassembly, you'll likely need to cut the ends off your drift to clean them up. More important I think on reassembly since you don't want trash getting into your bearing or fresh wheel grease.
Mentioning grease, I filled the cavities of my wheels after assembly but prior to mounting. That way I didn't need to use a grease gun to pump them full on the vehicle. You should also test your grease fittings before reassembly just to know they are unobstructed while its easy to see stuff coming out after a single squirt with it all apart.
Fun stuff
