Ok, i think i've got the starting problem sussed out. Took the diaphragms and the choke mechanism out of the both of the carbies and it seems that the choke passage from the plunger to the diaphragm chamber (where the fuel leaks down to be ingested by the bike) is blocked on them both. I used air pressure and didn't quite manage to clear it, but i have at least identified *THE* reason why this thing is being such a bastard to start.
Sorry for drawing this thing out so much, appreciate the hints and suggestion, some have proven to be very helpful. Will let you know when i get this fugger operating.