The best thing to do is keep the original drivetrain to sell with the car. It sounds like your 17 yr old will sell it in a heartbeat if he ever gets the pink slip in his name. I don't care what kind of drivetrain it runs these cars are old technology and need constant maintanence and upkeep especially if he drives it like most 17yr olds. My son and I build a hot rod when he was in high school as a project because he needed the focus. Well that was 8 or 9 years ago. He's been off a college for 7 years(still has a year to go), is getting married in a couple of months and it is still sitting smack in the middle of my garage and doesn't look like it's going anywhere anytime soon. Man, I could really use that space!! He doesn't want to sell it because we put alot of time and effort into it.
Just my $.02. Do what you want.