whats my Horsepower gain with these mods?

other than maybe a little better throttle response, I'd have to agree with 73a, probably 5-10hp. Its not going to be as big a difference as you'd expect. Brand new, and i may be mistaking here, but the 2bbl engines produced around 10 more hp.

Hows that 40 flowmaster sound? I've been toying with the idea of splitting my manifold and running duals with the 40's on my slant for a while now. I think it'd sound good.