Bit of an update. I've always fancied trying to make a seat, but I'm fond of the covers that have been on the car for the last 15 years. Anyway I've fitted a new 5 point harness and needed to fix the 5th point through the seat base,so decided to bite the bullet.This is the original seat
I bought a sheet of 1.5mm ali and some pop rivets plus a couple of hole punches off the bay. I used a scrap bit of square tube as a former for bending and did most of the cutting with tinsnips.
I had the original seat covers turned into loose cushions by the trimmer who made the originals,and used them to dimension the seat the seat.This was the result.
Needed quite a bit of tweaking to get the strength in it. I fixed it to the floor with bolts welded to strips of steel glued to the seat base. The seat cushions are a tight fit so didn't need retaining in place.
Fitted in the car with the new harness and some judicious blocks behind it for extra stiffness. The new harness works well,you really feel part of the car with it tightened up.