Thanks Dom, John and and Robert.
Dom, I didn't think of Bolex as I assumed they wouldn't sell jigs (yes daft of me) so thanks for that as the gate alignment jig is one of the two I have perhaps identified as not being able to make substitutes (I'm assuming you mean the jig for checking the alignment of the claws).
John & Robert, I have had email contact with Roger Sharman and he very generously gave me some tips as well as allowing me to ask dumb questions. I think he painstakingly put together his jigs over years including making some but and I remember him telling me there is one jig you must use or make to specs otherwise you can break a central part of the mechanism. He very generously offered to sell me a 16M body to practise on but I have gone down the route of a turret Rex camera which I have triumphantly extracted the mechanism intact.
Appreciated