Single speed tranny w/ lexan cover and motor mount.

[Gee]

SnoopMaxx, I don't know for sure to be honest with you. I haven't messed with a two speed in a real long time. Never had the new 3905 tranny to mess around with or looked at what the two speed conversion they have looks like.

There have been people here at RCM who have successfully drilled a hole in the 3906 shaft and used the revo slipper that way. Mike sells steel idlers here. You don't need to do any mods to get them to fit either. They work great. That might be the best of option for you if you want your cake and eat it too.

I had to look over the 3905 shaft thread.
http://monster.traxxas.com/showthread.php?t=412386
The first picture in that thread make it look like the gear could be in the right place. You would need to drill the shaft to secure the gear. Again I'd get MIkes idlers and save the the hassle of trying to get those two oversized (wide) idlers in there. First get the shaft and see if the gear will fit on the 3905 shaft in the right place to mesh with the gears first.

Good luck and let us know if it works.