I think it probably is Rod although I have no evidence to back up the claim. What convinced me was the rear deck arrangement on my friend's Sprint, which had always been a dhc and yet had exactly the same moulding as mine would have after the rear roof pillars had been cut away. And of course the hood tray, moulded specially to fit into such an odd arrangement.
If you think from a manufacturing viewpoint you could easily mould a body and finish an inch or so up the rear pillars/B post and then add on the top header rail for the top of the windscreen. That's all that happened with my car, plus of course some reinforcement at the windscreen pillar bases.
One set of moulds, two styles of cars. It's Chapman all over, isn't it ?
Brian