Fortunately, and all credit to him, the seller, 16yr old nephew of the deceased, knew as much about Douglas bikes as myself and has made several swaps to the "spare engine" and handed over enough bits of Dragonfly engine to get by, well mostly. I now have a pair of pots and heads that will probably work and he swapped the gearbox for a correct one with the inlet manifold, sadly the numbers don't match but are close. The deceased had several Douglas bikes and generator in pieces and all were mixed up so I got to pick through to chose the best bits in return for the T35 bits I can't use that will probably go under the hammer shortly.
We couldn't find a pair of cam followers and we only found 3 out of 4 of the push rods but I must say things are looking better
Still missing the headlamp, speedo, throttle and carb but I expect these can be found, eventually.