The B303 is not a great blower cam. With a blower I would use the OE cam before the B303. Th B303 doesn't make much more power than the OE cam. I'd put 1.72 rockers on the stock cam and set the blower to 7-8 psi unless you can plumb in an intercooler then I'd go to 12 psi. It should get you close.
If you decide you want to part with the B303, I'd be interested in it for a future non-Mustang project I am gathering parts for.