I took apart the seats on an early S1 and found they used two different styles of spring supports. I’ve never seen the style on the right. Interesting so I thought I would share.
Both my seats have the long springs. Most of my car was S1 apart from the dashboard.
The very early S1s (first few hundred I think) had slightly different seat frames from the later S1/S2. The back rest angle is also slightly different between the two. When purchased, my S1 (unit 150) had one S1 seat and one Corbeau racing seat, so the PO gave me a seat from an S2 which allowed the comparison. Subsequent study over the years of very early cars seen at LOG and other events helped illuminate this difference.
My early Elan, 0045, had one of each seats also. A friend had an S2 that was a dedicated auto cross car with racing seats that came with some original seats. One was S 2 and one was S 1 like my early seat. He gave me the frames. I ended up using the S 2 seats because one of the S 1 seats had a bad twist in it. I have saved the S 1 seat frames against the future when I can straighten the warped one. Maybe Gary