I installed Mazda MX5 (Miata) seats after modifying them a bit to be able to install them lower and have more space between my head and the roof. They also allow you to be further from the steering wheel because the shoulders can move back further.
The shape is a little too modern for the 70s but they are very comfortable and above all they have good lateral support.
I mounted them without slides, always to gain height and I had to make new fixings in the floor
I of course keep my original seats carefully packaged.
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