I have Cobra classics in my '70 Matic. OK fit but their original foam crumbled to powder. I had them repadded by a local trimmer.
I have fitted Autotechnica low backs to a couple of cars using their supplied runners and some custom attachments. They are good value but if broad of beam you may not fit. They are slightly narrower than Cobras.
A 1970 car should not need an engineer report. These seats tilt as original.
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.