Thanks for the link Ray O, it was what I had gotten from Gregory's, but.. The problem was with the distributor orifice itself. When I bought the motor, it arrived dripping oil as it had fallen over in transport. It ad bent the gearbox/back of the crank cover plate and put a ding in the distributor housing. This had in turn "out of rounded" the orifice. So with some brute force and a some vigorous rubbing (ohh, er) it accepted the dizzy!
Yippee!
Now only 300 other things to connect up!
Cheers
H