RE: aluminum diff
Yes I did the 4 spider mod and I'm using kyosho bs107 bevel shafts. I've packed my rear diff with vaseline and my front has mobil 1 synthetic grease. I thought I'd try something different just to see how they hold up however I'm a firm believer in not using fluids in the diff due to leaking. If I were you I'd keep the truck mostly stock otherwise except for the brakes. Definately upgrade to the hpi dual disk setup if you haven't already and use machine threaded screws instead of the self tappers. I'd also recommend that you keep an extra tranny one way along with the two speed drum and maintainance kit because sooner or later something is going to give.