Before I set out on that kind of project, I'd visit a guy I met who lives in the UK. His wisdom, which I figured I'd share here, is that the hard part is getting the interior items all in good working order, and separating yourself from the outside (good doors, seals, windows, and all of that).
His solution was to find a brand new car. Not one that was very "stylish", but very functional from a ergonomic perspective, and use all of that "cabin", but throw-out (actually part-out), the rest of the new car. Then he'd put that on a frame with a performance motor and make a sexy body for it. Then, you've got yourself something you can drive in comfort.
He's done this several times, and said he's written articles in magazines about his experiences. When I said he should offer kits, he said, nah, then you'd need to talk to customers, lol!