Yea... There is this nice Swiss guy who made a few a while back.

I think there are a couple more folks around here that have these as well.
Only downside to the true center diff on the revo is in most cases they force you to run with the truggies. The Monster trucks class usually requires a transmision of some sort. At the RCM Bash last year I had to run the Revo in the Truggy class. I was pretty happy to get third place with it racing agaianst the true truggies.