If it were me, I'd not worry about the vacuum and the "driving" part of the engine. I'd cam it to turn some revs so that it will be efficient and make some horsepower. A solid cam with about 240-242 duration @ .050", a 108LSA on a 104ICL, and about .600" lift.
In stock form with the Boss 302 cam (about 228 deg @ .050"), it should make about 375hp at 6600-6700. You could probably get closer to 400 with a little larger cam and a higher peak, but prepared for less and less torque. A stock 5.0 Mustang had more torque than these Boss 302's did.