I've got an '83 Camaro cheap. Other than the drivetrain ('88 350TPI/TH350), what is of use on a 1st gen Camaro?

Possibly the steering box. It "might" be a faster ratio, and/or have a heavier steering wheel effort. If you find a good box, you will enjoy that upgrade. If the car has rear disc brakes, you can also swap those onto your 1st gen.

Other than that, I can't think of much else that would be an easy swap.

I've seen the seats used. You can get new covers, even leather.