Ah ill put the shims back the way they were then, I'm second guessing everything as I've never heard the motor run and there was parts missing (idle gear etc). 

Just managed to find a manual with the crank specs so ill get it all measured up with and see how it is. I'll check out PJME, difficult to know these days whats decent quality.

I shouldn't worry you but rod can feel within spec but be breaking through the hardening & sound like rough mains when running. I'm sure you'll be ok but I'd revolve it by sliding the crank into the easy side Right Side bearing then fingers on the small end rod eye & revolve it & you'll feel any roughness. If there 'is' then flush it out & oil then try again. How were the main bearings, mag side suffers more than the right side.

Thanks, I measured the rod play and it comes out within spec, but towards the higher end. Crank is running nice and smooth using the method you suggested and there’s no rough spots. I’m reasonably confident in reusing this crank as is, but if I can find a decent local shop to do the rebore, I may get them to give it the once over anyway just for peace of mind.

main bearings were fine, given the condition of the rest of the bike and the fact it had obviously been a field bike I was expecting everything to be a lot worse. Although it does look like it’s just been sat rather than abused too much.