Exhaust limits/Carb choice

First car huh? Well I put the exhaust manifolds back on. 2 inchs isn't much and you know how kids are sometimes. Yes he has lots of motor bike ex. but out in taffic is not the same. He needs time to learn. Sounds like you are a great dad, some just get them a POS at first and get a new or very nice car for themselfs. A 360 with 3.55 gears in a lightweight 67 dart is going to be fast enough for the first year or two. Headers sometimes leak and make lots of noise--not that hes not going to want a pair of cherry bomb mufflers anyways-so I would just find a early set of 360 factory manifolds and make sure the heat raiser is open or better yet remove. With a dual exhaust it be fine. I also stay away from the DP carbs, yeah they are ok if you are in the right gear but again he needs to be watching the road not worrying about what gear the car is in. Sorry if I sound like a old fart but hes very young and has lots of time later on. That still will make a great first car for sure and if he takes care of it he can go all out later on. Just my 2 cents