HOW TO FILL A DRY COOLING SYSTEM WITH NO AIR LOCKS

I air locked a 440 once. ALL you need do (and the stat vent hole is a good idea) is to disconnect the heater BELOW the T stat on the intake. You say you don't have a heater, but you DO have a pipe plug there. Just remove the plug. Another way would be to pull off the top end of the bypass hose.

If you don't have sealant on the t stat housing, you could also remove the water neck and t stat, "gently" crimp the top hose and tie some twine around it while doubled over, etc, and then fill until you get coolant up in the t stat area of the manifold.

Still another way is to temp install a petcock/ valve in the lower heater hose fitting at the manifold to bleed it.