It doesn't phase me too much doing a conversion on an original car. I've always reckoned it is better to modify (not body wise but unboltables) a valuable car to start with. I'd rather use a Sandman as a slightly modded car than a 6cyl base model as an injected conversion does bugger all to hurt a Sandman. I wouldn't stuff with a totally original Sandman with all original driveline, but if it didn't have its original engine or if it was only a 202 or 253 i'd much rather a Chev or stroked 308 or inected 5litre than another non-original engine. If I wanted a van i'd buy something like the Valencia Orange car Adam had, make it look totally stock and run it with an injected engine rather than just use an old stocker. That's just me though, I like originality but only if the car has it already, to me it is a waste of time and money to build something back to as it was when it is cheaper and easier to improve it!
I know its a lot of work to weld up window if you want a van without them, but it is still shoads easier to do that to a good rust free van than it is to replace cowls, floorpans, lower quarters, drip rails etc.