Don't believe people telling you 30-45 HP all across the curve, simply not true. With 8:1 low comp pistons and that can, you just lowered your static camp is probably 7.5:1 if you are lucky. Real world numbers on a Dyno would shock me if you got more than 15 HP and that would only be above 4000. Below that rpm I would expect 8-10 max. Unless you like spending your weekends swapping gaskets, I would stick with manifolds.