First, thanks for your replies! Further status:
1. We have a very capable soda blast business very near my house, and they did try a sample area soda blast on an inconspicuous area of one of the shells. The process seemed too hard to control with the large nozzles, and they were not able to perform the paint removal without risking considerable damage to the textured fiberglass surface. Recently, however, this business added a new glass bead blasting capability to their arsenal, which may be important, since:
2. I found an old video on-line that showed the refurbishing of 1978/79 to 1982 seat shells, and they used a very fine, very low air pressure glass bead blast to remove the old paint. The local business has the video, and plans to try another test with the glass beads, hopefully this week (they have entered their super busy season).
3. Thanks for the note on the use of 73-74 rear seat track brackets to convert to the 74 floor bolt pattern, which I had already encountered on the Web. Interestingly though, my car still has its very rough fiberglass seat belt retractor covers under the seats, which, coupled with some issues with the carpet, seem to require a shimming of the seat tracks to clear these obstacles. Shimming is a very bad idea, of course, because it decreases the already-tight headroom in the car. Did you find any such issues? Note that my current 78-82 seat track complement consists of (2) sets of identical configuration tracks, that I believe to be passenger sets. These tracks all have a "C" shaped metal bracket which is about 2 1/2" long at the front of the track, where the seat shell bolts on. These tracks thus also have a very low profile front bracket, which bolts the track to the floor of the car.
4. I believe that driver side tracks have a full-length flat top surface, with a much higher profile front bracket which bolts the track to the floor. I'm trying to get at least one set of these driver tracks, which should be here shortly, to see if that makes any difference in clearing under-seat obstacles. Unfortunately, my trial fitting of this stuff is complicated by the fact that my car is on a lift in the mechanic's shop, and is thus only available to me at certain times!
Thanks again for your help.