when i had my bigblock nitro tc3 i tried to swap ofna diff stuff in, however couldnt find any info and it didnt seem like it was going to work. i managed to find a company called Dynotech racing, they used to make a drop in aluminum ring and pinion for the nitro tc3. i cant find it on their site anymore, but it might be worth e-mailing them. here is a link http://dynotech-racing.com/
they work well, stood up to my rossi .21 just fine. i now have an os .40 4 stroke in the car and they are doing alright. lubrication is the key with aluminum gears, along with shimming. im now actually running some 80w140 gear oil in the diff housing and it seems to work well. after all this time though they are starting to wear and im going to have to replace them. if you do email them, post up hgere and let me know if they still make them.