What oem said.
I've had a pick-up seat in my Suburban since getting it 4 years ago. The bench DOES tip forward, so kids can climb in the back.
All the seats are difficult to find, but once you start looking, you'll come across them.
Same deal with the tail gate. You'll find one, but it'll take a while. the barn doors are more common. I've got bard doors on mine, but am thinking about converting to tailgate/lift gate. The doors are convenient, but I'm tired of the wind slamming them on my elbows. Plus, you can stand on a tailgate at races, sit on it, and it makes a good work platform.
The sliding rear window latches are also hard to come by, but again, they'll turn up once you start hunting.
I LOVE my '62 Suburban... it's been a work-in-progress for almost 5 years now, and it's been my daily driver the entire time.
-Brad