whats wrong wih the stealth thats in it now? Definitely rebuild the dif and go from there.
Mentioned above it can me modded to take a better slipper assy. Unless the shocks are junk they should clean up. Paint is easy enuf to clean off of them and rebuilding shocks are definitely part of the RC experience
MIP CVDs are all over ebay for these things. Many different associated truck models will work with this truck.
As cheap as the RPM parts that were linked above, again a personal opinion, I would just get new so you can eliminate slop from the wore out parts you'll pry find with used.
There are infinite possibilities with bodies depending on what you want it to look like in the end. Might have to get creative with body posts and mounting ideas but pretty much anything can be done there.
If I were you I'd limit myself to 2S lipo. A 3S will definitely be overkill unless you are trying to kill this truck off completely. Lipo is definitely worth it though with your choice of electronics it should be a great project for your son...and you
Good luck with the project. From the pix it looks like it could be a solid foundation for a nice runner for Junior...then you can get one to run with him and do it all over again
Todd