F.A.S.T. Hemi's are getting 1.5 HP per CI with original heads, intake and exhaust manifolds, AFB carbs, and cams the idle smoothly.
Take away any of those limitations, and a Hemi will really fly!

Hemi's really love stroker cranks and big cams.
If your building a hemi from scratch, there's no reason to stick with the little 3.75 crank, unless you are working within a set of rules that require it. The price ends up about the same for a stock or a stroker crank.