Seats from a Porsche 914 - any year - will fit like they're made for it. Make sure you get the seat glides AND recliner stuff to go with them and you can have both sides bolted down in well under a couple of hours and then they're adjustable!! I used a couple of 1/4" thick by 2" wide straps across the underside of the pan under the seats to run the bolts through and give the whole assembly more strength. Makes them feel much more solid.
914 seats all came with integral headrests, which I need, but the headrest can be easily cut off and a decent upholstery shop can modify the material to nicely cover where the headrest was if you prefer the lower seatback look.
Can't help much with the exhaust. I have a Berg Dual Quietpak (GB932?? - it's been a while) and it doesn't hit the body but hangs a bit low. Other folks are running A-1 systems, but first you have to tell us what you have for an engine displacement, valve sizes, what carbs and cam.
Where are you located, Brenda? Someone might be able to point you to a good Porsche salvage yard nearby for the seats. I got mine from the 356 registry years ago.
Thanks... gn