As stated, some pictures will help. You probably have quite a bit of work ahead of you before fiddling with the engine/outdrive. You probably want to understand if there are any horsepower limits to the Wellcraft model that you have.
While you are rebuilding the boat, you can keep an eye out for 7.4 engines and Bravo outdrives, transom assemblies.
Got a budget in mind for all of this?
As for the cap . . . the pictures would help. But usually I/O configurations can be done without removing the cap. It sort of depends how much of the boat (cockpit/sole) is part of the cap. 1991 was during the transition of boat design where the cockpit/sole became part of the cap and not part of the hull. . . basically 2-piece construction.
