I find my self always looking at the seats in new cars these days wondering if they would fit in my convert bird.
I know the guy that did the 2004 GTO interior in a 69 used BMW M3 seats I think. They look really good and have the built in seat belts.
I was looking at a mini cooper at the mall and noticed the seats are very narrow in that car.
I also rode in my friends chevy suburban. It had nice seat belts built into the seat and a flip down arm rest. I really miss having a good arm rest in the car on long trips.
I looked at some 69 grand prix seats one time and they were way to wide to fit.
The pro car seats they sell through summit and other places seem like a good way to go. They have a retro look, side support and not horribly expensive. I still like some of the percs that the newer cars have with built in seat belts.