[BigBlocksRule]

Those are small port heads, made for max torque on the bottom end but they'll run out of steam around 5000 rpm's. Better heads are open chamber ovals, look for the last 3 digits to be 781 or 049. They're fairly common, expect to pay about $150 for a pair of cores. The ones you have can be made to work with some porting and bigger valves, but the castings I listed are much better from a performance standpoint.
That block is one of the more common ones, should be a good one.