My friend has a 79 Malibu with Cobalt SS seats that he really likes and his son's regal has newer GTO seats. I personally think the GTO seats look to big in the car.
I have a set of Cobalt SS (Recaro) seats I made work to bolt in to the g-body mounts using feet off g-body tracks. Still haven't had them in besides test fitting to see how I like them but they look real good IMO. I agree on the GTO seats being a bit too big for the g-body interior.