The hot rodders do this all the time and call them "coupsters". I don't get it, I always thought the sport coupe was one of the nicest looking Model A body styles made and there is no reason to make a roadster out of one!
I agree with those who say "Why spoil a good Sport Coupe to create what would be a terrible looking Roadster?" If you want a Roadster, buy one and sell the Sport Coupe to someone who will appreciate it for what it is, a sporty, good looking Model A coupe.
novaki,
I have a doctor friend who did just what you asked! He had a nearby rod building shop make a "coupster" (they called it) out of a '29 Sport Coupe. The doc was very enthused about the 'build'. I have a '29 Sport Coupe plain jane..like henry rolled her off the line yesterday! I asked the shop owner to look her over and tell me how much to 'modify' her...like the docs. To my surprise, the shop owner says...'nah, wouldn't do that to this car'...Go figure!!