Thanks all for a very interesting thread.

I'm very envious of Woodsy's early SLR. Sadly, I currently can't own one due to it's military pedigree and my location, but I'm working on it.

Back to the original question, the bloke got back to me on the origins of the drawings and I quote; "It's a copy of plans for a DMR version of an SLR, tested and trialled by Lithgowicon in 1973, before the term DMR was invented".

DMR to the best of my knowledge stands for Defence Materials Review or something similar. Something akin to our current DSTC.

Thanks again to all the contributors to this very enjoyable thread.