Last piece of advice.... don't do it. Your current RC will never have good DNA. Use it as is. Instead find a good used RC or pony up for a good new one but don't put money in a car that will never have a future.
To be at all a good car it would need to have a brushless esc, brushless motor...
Honestly it seems that you should approach one of your son's friends (friend's Dad) first to see what sort of RC that they are using.... your son will almost definitely want to do the same type of driving so they can play together. 100mph cars are not usually what his friends would be pursuing...