Welcome. The 87-93 Gt's came with E7's. If you could find a set for cheap it might be worth swapping them, otherwise for a few hundred dollars more you could probably find a set of GT40 heads which would be a much better swap.
The B303 cam is a hydraulic roller. If the car has the original engine in it, it will be a hydraulic flat tappet. There are conversion kits available, but you would probably be money ahead to find a flat tappet cam with similiar specs.
Good luck with your sisters car! Sounds like a good time for a V8 swap!
andy