Will they fit? For example, if I want to sell my Iroc but keep the new '97 SS leather seats out of it for a '69 Camaro, will they bolt up?

3rd to 4th and vice-versa is an exact match.

I don't think they will bolt right up. You will most likely have to fabricate a bracket to get them in.

There is a guy on this site who grafted in a pair of leather 4th gen Firebird seats and console in his '69. Looked suprisingly good!

Use the search function on the upper right hand corner of the screen, you might be able to pull up the post with the pics.