For anyone interested....
Its up and running and moving under its own power (although not road legal yet). I was able to move it around on the driveway on Sunday morning.
A number of small, but crucial, parts went missing from the box of bits (e.g. pins for the clutch, bespoke nuts and washer for the clutch and even the key) went missing between looking at it and collection

. Fortunately I remembered a friend in Derby had a gearbox (very rare) which would have the parts needed so I grabbed that on Friday evening - which yielded some needed parts, the rest I had to fabricate (e.g. buy some 4.7mm drill bits and cut the ends off to make the pins).
It would have been running and moving on Saturday if the tool I made to install the clutch springs had worked correctly - but once I realised what the issue was - percussive maintenance sorted out the tool!
The clutch plates that were with it are wrong, and wouldn't last long and would cause damage. Fortunately I had the correct clutch plates in stock and know how to recork them!
A few pics (and vids) here if anyone is interested. It includes the tool I mentioned earlier.
https://www.dropbox.com/scl/fo/qsqx40ji ... mui8c&dl=0