Here a set of aluminum cups already setup. Doubt they have the improved internal gears of the 3905 but they are an considerable improvement over stock. I ran a similar setup in my FLM maxx without any issues for some time.
http://cgi.ebay.com/ws/eBayISAPI.dll...m=120429907461
I'd guess the final price might end up close to be double of what the current bid is right now.
Is the 4908 T-maxx the improved on they put out after the 16.8 e-maxx? Makes sense they use the same beefed up diffs.