wyrmrider is right that the pistons are the problem.
Even if you put the small chamber B-1 B/S heads on that are 65cc chamber, compression is still only about 9:1 compression ratio, and those heads are expensive and take an offset intake rocker arm.

I am helping Dan (Colorado Mopar) with his 440. He was thinking of using the 75cc Edelbrock E-Street heads (for cost, and about 8.4:1 compression) and mild cam, but when we checked the crank, it is shot. Over 0.004" clearance, rough surface, posable it is not even straight? Cast crank that would need to be cut, polished, balanced. After adding up all the costs to recondition the crank, rods, and change pistons we were not too far off from just getting a stroker kit, so now were going to do a 4.25" stroker kit.