no the hpi rs4 supper nitro has a 2speed upgrade that MIGHT work, key word might, and if they still even make it/anyone still sells it. time to upgrade dude to a new car. The r40 transmission and clutch setup are totaly different from the rs4 2
no the r40 tranny wont bolt right in, however you shouldnt have any trouble finding a 2 speed for your car. i just built 2 of these cars last winter and didnt have any trouble finding parts.(both are 2 speed) if your local hobby shop wont find a supplier try another hobby shop. there are still alot of these in circulation, ebay is another good source for parts.
i just picked up an rs4 nitro2 and they guy i got it from put one it. i have the paperwork from it around ill find it to let you know what it is exactly