If it only runs well enough to idle and won't accelerate, then that is a HUGE pig in a poke. I would ask for previous work documents that could be verified. At a minimum, if it hasn't at least had a top end build and lower head stud replacement you'd be wise to spend $30 for a valve cover gasket kit and remove the lower valve covers to see if it has any broken and or missing head studs. Your $2500 repair budget would increase by a factor of 3 or 4.
should there be problems with the studs. With what you know now, I would tread lightly at best. And yes, I own an 82SC coupe.