'68-'70 Coupes - all Belvedere 2-doors, early-'68 RRs - zero Belvedere HTs.
Coupes have a full B-pillar (rocker to roof), HTs don't.
Coupes had pop-out quarter glass hinged at the B-pillar, and different door glass & upper weatherstripping.
The differences can't possibly be worth doing a conversion.
All Superbirds were HTs, zero Coupes.
Superbird conversion also requires the nose cone & headlamp stuff, Coronet fenders & hood, back glass plug, etc etc.
Every once in a while a clone-Superbird project pops up for sale.