Forget the long stroke engines. No need to use more than 4.25, the long stroke motors using the same heads doesnt run much if any better. I have built a few big bore and long 4.5 stroke engines both Hemi and wedge. The longer stroke is harder on parts for sure, lots more piston speed etc.
Build the largest bore engine you can get, use a 4.15 or 4.25 stroke, light weight stuff, and spin the engine some.
I would NOT use those heads in a "Ultimate Engine" however. No reason that they couldnt make 850+ HP pretty easy N/A though.
Set some power goals, and build around the heads.