Peter,
First of all - please dont jump on the kickstart - it is the weak point on the Dragonfly engine/gearbox unit, and you could end up wrecking the gearbox case.
From your comments, I think you may already have located the problem - with the generator cover removed, the crank turns OK (with or without the gearbox attached) - so the problem is likely to be within the timing chest. First thing to check is the crankshaft nut - this should be a thin nut (like a locknut) - a standard nut is thick enough to foul the crankshaft outrigger bush in the generator cover. Check carefully that there is some clearance between the nut and the bush - due to the direction of rotation, if it does drag on the bush, it could get unscrewed and jack the generator cover off the timing cover.
Regards,
Eddie.