I've always felt safer with more modern seats/headrests and have made multiple attempts at non stock seats but never been happy with the results. My apologies for the long post, but I have a bit of experience in this area.
Many years ago I installed a set of TR-6 seats (the one year that had the fold down headrests) and drove with them for a while, but they were really too big for the car. The were easy to mount, as they had the same kind of pivot mounting as the Alpine. I know a lot more about fabrication today than I did then and would like another shot at them, but sadly they are long gone.
My next attempt were early 70's Fiat 124 seats that were given to me by a friend who was junking his parts car. These looked great - like they belonged- but like the TR seats, they sat too high for my comfort, no matter what I did for mounting. It might have been possible to make these work, but they needed to be completely rebuilt (they's sat outside in the rain for a while and stunk!) and I didn't want to invest in seats I didn't think would fit right in the end.
At the moment, I have a Procar Rally driver's seat in my SV. (
http://procarbyscat.com/seats/Rally) I really like the way this seat looks, but guess what? It sits high. I've had it there for a little while and have gotten used to sitting a little higher, but the seat is very firm and just isn't comfortable for me. I visited the Procar office while in California a few months ago* and sat in a prototype version of the Rally seat that was wider base and softer padding. That might be a good option if you don't mind the higher seating position, but I am not sure they have released it.
My final attempt will be Miata/MX-5 seats, as others have mentioned here. I have a set of the M-Series seats with the removable headrest (for me, that is a requirement for non Rootes seats, both for looks and to allow removal when using a tonneau cover) that I temporarily installed in my SV a few years ago. Like everything else, they sat higher than stock, but not too bad and I think I might be able to get them even closer with some more fiddling. My plan is to use these in my V6, whenever I get to the point of getting it on the road. They will need to be recovered, so I won't tackle that until I have satisfied myself with the installation.
So, a few final thoughts for anyone heading down this path. First, expect any non original seat to sit higher than stock. Besides my four attempts, I have tried to sit in every Alpine/Tiger I've seen with aftermarket seats and all were higher than stock. While this doesn't bother many owners, it doesn't suit me. There may be something out there that works perfectly, but the only alternative I can think of is to modify the brackets on the floor, which would be a pretty major undertaking. Second, if all you want is head restraints, there is another option; two actually. Bill Blue has modified his stock seats to have a headrest and that looks like a good option if you are recovering them anyway. The second is what I have done, which is to install a roll bar that has a provision for head restraints. I can post a photo of mine if anyone is interested, but I think this is a pretty good option. I am in the process of rebuilding my original seats (repaired frame, new foam, etc.) and will probably just stay stock in my SV. Hopefully, the M-Series seats will work out for the V6.
Jim
*Just one more note for anyone interested in Procar seats. While the seat isn't right for me, I cannot recommend the company highly enough. I bought the seats years ago but it was only recently that I made a serious attempt at using them. In the process, I'd lost a piece of the plastic trim. I contacted the company to buy new trim, but instead they just gave it to me. I spent most of my career helping companies improve their customer service, but don't think I could teach Procar a thing!
