There are a few 3905 alloy tranny cases out there... cant remember the name of the brand but you can find them on ebay, just do a search for '3905 emaxx' and you should locate them easily enough.
I think the UE super shocks/ ofna buggy shocks are on the smaller side, so maybe 16mm diameter? 4 shocks is fine, you will just have to use slightly stiffer springs probably and take some time to tune the suspension to your liking.
Like Rivermaxx said though, it makes much more sense to buy good condition or new assembled shocks from ebay, rather than a kit from towerhobbies that will cost more than twice as much. Save your money & time!