with a Big block with the right heads and cam (and bottom end) you are talking alot, when you say BBC you are looking at a capacity from about 454ci to 572ci in crate engine form from GM.
Say you are going for a reasonable spec 572ci (about 9.4 litres) running say 850 bhp n/a on a very mild drag spec engine you could probably expect to sove another 400 to 500bhp into it as a nitrous shot into square port aftermarket heads, alot more with the right cam, heads and bottom end. Similar but in proportion to displacment for the 460 ford. How many bhp do you want?
Mike