Thats an RC10. Very nice. You can rebuild almost anything on it. The first thing that you should do is buy a $4 shock rebuild kit and $2.50 shock oil in 35w. It will make an incredible difference on a buggy that is that old.
You dont want to put to much power through the buggy because of the age of the transmission. You can buy new ones from RPM but you will need some old parts out of the old one.
Almost all modern buggies have bearings, and not bushings like the RC10 had. If you still have the bushings, buy a complete bearing kit. Dynamite has them and its not to expensibe. If you put a faster motor in it, you will have trouble with the bushings overheating.
Get your self a 19t komodo dragon motor for $25, and a good battery pack is important. The higher the mah the longer the run time. Get a good nimh pack for under $40.
Good luck rebuilding that buggy! With the upgrades that I mentioned above you can make it very quick and moderenized.