I think the only problem as you say with the rear is that it doesnt look sporty enough.
Thats why to do this conversion properly all the way would be to use the shorter style sedan boot which slopes not points up like the wagon. I still would love a roadster as you say like this and although it wouldnt make a long distance tourer it sure would be better than gong long distance with a hardtail harley. however you need something to stop the high protein bug diet and the little screen could help as long as the seats are nice and low mounted. My previous roadster picture had the little motorbike windows and was based on the sedan 2 door. If I could have a roadster, a van and a coupe Id be in heaven.

With the short sedan trunk & a shorter wheelbase so that the rear wheel arches intrude a little into the lower rear of the door, it could make a good little roadster.
With the top removed from a two soor sedan, on the stock wheelbase, you have a convertable, but i still think the roadster concept shows more promice from a styling point of view.
Basing it on a '67 model, as you have, is a nice touch.

The hardest thing to find and although not many like them grilles they are my fave.