Phil, you are stretching my memory a bit but I am sure they will fit.
I bought a very cruddy set of GTO seats with both the recline and the headrest options for my '66 Grand Prix. I would not like to even start thinking what they cost me to import them over here. They came by air!!
I pulled them apart and fitted the head rests into the seat backs. I had bought some original vinyl from SMS in Oregon to recover the head rests.
For the recliner, I also stripped out the mechanism from the junk GTO seats and fitted it into my original passenger side seat. The handle is the same for GTO and B Body. Just be careful the recliner cable is running free and smoothly before you put it all together. Otherwise its a pain to pull it out.
None of it was difficult to do. At the same time I did all this, I bought from our hosts (PY at the time), a set of new seat foams to complete the job. My car was originally ordered with the electric seat base so I now have every bucket seat option available in the car. My wife loves the passenger side recliner as she can sleep easily when we travel long distance.
On the other hand, if you want to use the GTO seats, I think you only will need to use your existing seat runners from your seats and fit them onto the GTO seats. Just a bolt up job.
Ian