Hi Lewis. I had a look at that document and I have got part nos 66 and 67 on the bike and the two plates nos 69 and 70 so with your bit it seems that it is nearly complete. I see on parts 66 and 67 that it looks like there is a nut and spring on the end which I do not have, assumingly these return the pistons back home. I think I might actually have them unused and unneeded on my other bike so Bob is possibly your Uncle.
So with your part added and me having a look at the decompressor lever parts in the catalogue, my brain still can’t visualise how the bowden cable connects to your part and operates it and possibly holds it. That looks like a special lever which I can overcome I am sure and I can get a lever and a cable and I am pretty sure I have the frame mounted recess for the engine end of the cable. Is there a picture you can point me towards that shows the arrangement at all please. By the way Lewis I don’t have your number any more as my phone lost most of its contacts. I am on 07531781196. It’s probably more simple than I imagine or is it just a hole the cable goes through. Thanks again.