1973 Ford F-350 Water flow issues

I am having problems with a 1973 ford 360. First the radiator was blowing water out of the radiator. Changed the thermostat. Problem continued, then we checked the compression on the cylinders and found that two were significantly lower than the rest. So I pulled the heads shaved them, inspected both the block and heads for cracks and reinstalled. Also replaced the radiator. Problem continued, left the return hose off the radiator and ran motor for approx ten minutes, checked motor temp on block with laser and reached 370 degrees but the water flow was poor10-15% of hose diameter and slow and only reached 185-190. Pulled water pump to ensure all was well and there are no plugs, rotor is in good shape as well as the bearing. What am I missing? Could the block itself be plugged? How should I go about checking correcting problem?