RE: Outdated electronics
A lot of those old Radio shack and Sears cars were actually made by Taiyo. They were higher quality RC cars back in the 80's that often had proportional steering (unlike today's cheap New Bright/Fast Lane RC vehicles) This is a good thing, because as long as the proportional stock steering servo has a potentiometer, you can unsolder the stock wiring, and use the circuit board from a more modern Futaba/Hitec/JR/Spektrum style servo instead. This will maintain the stock steering setup; I did it with my Sears Offroad Buggy, and it worked great. The steering is the hardest part, so provided you can overcome this hurdle, everything else is gravy. The ESC is pretty much a no- brainer; just buy a cheap reversible brushed ESC (proportional both ways), cut the wires to the motor, and splice it in. Enjoy being able to use a hobby quality radio (and fully proportional control) with your vintage truck.