X O U or J heads on a 416?

What kind of power did they leave on the table ?
I imagine you could build a 416 and tailor the cam and top end to make use of the small port high velocity......probably create a relatively low r.p.m. torquey sumbitch too.
But a motor is still an air pump at the end of the day.
More air in , more ooomph out.
Years back I did some business with a builder who created a pair of 460 Fords that made peak torque at something like 1800 r.p.m. , they were destined to power generators in a large motor yacht. Had cams custom ground and spec'ed everything specifically to where these things were going to be run.
You can certainly use factory iron heads , though I'd definitely have them ported so they didn't choke things too badly.
You could probably do the calculations and get a ball park using this formula .......drop down to the H.P. from air flow and it will give you a pretty fair idea of what to expect.
Certainly enough power to make for a stout street car , and it would probably have reliability built in due to the restrictions the heads would place on the combination.
http://www.wallaceracing.com/Calculators.htm