It isn't the cubic inches, it's the heads' flow and how tight you're willing to turn the engine.

IIIRC there was a flow test published years ago, in some Chrysler magazine, where someone and it may have been Dvorak, flow tested a bunch of heads, then put a set of stock Hemi heads on the flowbench just for fun. I seem to remember the stock Hemi head flowing around 305cfm on the intake port, which should be good for 600 - 630 hp. But how tight do you have to spin a 426 to make the power?

That's why I say the Hemi heads needed a much larger shortblock under them to really work
Back in the day, when Hemi and 440-6 were both being produced, on of my favorite car mags of the time road tested a Hemi and a 440-6 version of the same car. The Hemi was running 3.54s, the 440-6 had 3.91s. The 440-6 was quicker than the Hemi in the quarter, which surprised the writers.
Now put a 500 cubic inch shortblock under the Hemi heads and it should kill everything with a stock head, and I mean everything.

With the numbers I have seen here, my recommendation would be to buy the Edelbrock or MP versions of the heads. Build the biggest shortblock you can afford. Then, if you need more power down the road, have the heads you have ported. There should be at least another hundred hp in that, maybe more.

I give this advice with the knowledge that I just bought a used car for daily driver that cost about as much as a set of Hemi rocker arms, shafts and whatever else they need to be usable.

R.