Re: 4th gen seat foam
The later model foam is a lot more resilient than 1st gen foam, burlap, etc system. So unless the car was owned by an exceptionally heavy person, extremely high mileage, or chewed by goats dogs etc, chances are very good the OE foam will be reusable.
Unless you are of very small stature with stick legs, you most likely will not want ANY added height that new foam could give. I tried 4th gen T/A seats (wanted the separate headrests so I could try to make it look more like 69 seats), and just doing the standard modification to the rear mounting points (just adding ears in the correct place, not welding them underneath or anything that would alter the height). I found that even with the seat in the down position (the seats I bought were leather but fully manual in all adjustments, even had the cool slide forward part to adjust thigh support), I sat too high in car and thighs were too close to steering wheel. I am 6-1, at the time just under 200, and I have a non-tilt column with an original GM cushion rim 3-spoke wheel. I drove the car for a while with those seats, and tried to convince myself I'd get used to them; I realized I would have to adjust the seat the way I cruised our Regal when I was a kid, reclined way back and arms straight out.
I looked at modifying the tracks to drop them, and between that issue and what I was quoted for new covers (was going to do leather front and rear, with the center of the fronts in the horizontal pattern of the 69s and the rear seats subtlety sculpted to look like the 4th gen seats; using the 4th gen rear seat was an absolute non starter for me because of the high tunnel arch of the seat back would have had me building a rear console, negating the ability to fold it down and just making it more of a custom than restomod), I decided to skip the 4th gen seats.
Then TMI comes out with the Sport foams for the OE 69 seats, so that is the way I went. Now if there was only a way to make them recline, and I really should have found the $$ to add the bladders for lumbar adjustability...
Point is, if you are aware of potential seat height issues, and can pay that little for a pair and just get ones that are not cut up, you probably will not need new foams. I would think worst case, and I am just spitballing here, buy two pair and use the passenger side bottom foams in both seats. Does that make sense?
69 'vert project big block/TKO 600 RR
68 'vert driver RS clone -- gone!