If you're bashing then that's a great deal, and the truck is tougher than any out there for this purpose.
If you're racing I'd just spend some extra and buy a gt2. The gt2 is pure and simple easier to drive fast than the old gt.
If you're looking for speed an os .18 with a short shaft would probably be your best bang for the buck. OS has awesome engines that are reliable and easy to tune. And you can pick up a new .18 for a good price.
Mugen engines are very fast though so you might not even need any more power or speed.
GT2 parts will not work as stated above. About the only thing the same is the diff gear and ball cups.