Those heads are great and I'm glad you're going with a roller cam, especially with today's low zinc oil. The problem with already having the heads and cam is that just buying an off the shelf shortblock, you may end up with mismatched parts and a poor engine combination.
I would contact a local engine builder and have them build an engine with the right combination of parts that meets your goal with the engine. I have had good luck with Kinectic Racing in Westland.
http://www.kineticracingengines.com/default.htm
Mike