On the Alfetta and I would assume on the GTV6, the seat back is held on with a plastic "wing nut" that is basically hand tightened onto a stud that is connected to the seat back frame. To get to the wingnut, the carpet that is against the gas tank has to be loosened on each side to get access. The wingnut and stud are very close to the top upper corner of the gas tank, Between the tank and the inner fender area and under the small ledge the cargo cover is hinged from. They are difficult to see because of the location but relatively easy to feel around and find. Once the wing nuts are removed you can push/pull the top of the seat loose. Than lift up and out to remove the seat back. Again this works on the Alfetta and I think the set up is the same.
easy actually, all you need do is lift the front of the seat cushion straight up (there are two plastic plugs that locate the cushion into the seat riser, the back seat has two flat locator prongs on the sides that slide into slots (at least on my '81 '6 and from memory. mine's been out for years as I always needed access to my harness sholder straps.
Thank-you very much for your response to my back seat inquiry. Yes, the base is held to the car by two prongs, opposite ends of the base and forward, that push through retaining grommets in the seat riser, allowing the base to just pry up forward & lift out. The back is held in with two metal strap type tabs on the outside ends, which index into attatched slots on the inner wheelwell. It is also held in with two metal studs in the very back and upper, or shoulder area. These studs drop through slots in the crossmember between tank and passanger compartment. Both studs were loose and missing their plastic or rubber sleeves. The repair, with the help of my wife, took 20 minutes, and sent us back down 128 in the tight quiet GTV6 it had always been. Thank-you very much for your help!
Fred GTV6 VROOMA