I converted my RTR over courtesy of flebay. The diff gears are the same except for the spyder center obviously. Now I have friends that I race with and they don't use the spyder center diff. One of them works over at Nitrohouse and he's the one that has provided me with lots of helpful information. He said it was ok to use the stock rtr diff. As a matter of fact one of them uses a kyosho diff and the other uses a jammin diff. I haven't had any issues with my center diff. Is the spyder diff going to make you go faster? I don't think so. Run the stock center diff and fill it with fluid instead of the grease and you will notice a performance increase. I removed all grease from the RTR diffs and fluid filled them with 7k in front, 10k in center and 2k in rear.