That is an interesting question.

"bock drains" - could have been two petcocks, or one petcock and one threaded plug.

The 1955 and later Owner's Manuals refer to the drain cock on the right front of the radiator and the drain plug on the left rear of the 6-cylinder block.

"Both" (two) drain cocks are referred-to in the 1954 and 1955-2nd Truck Shop Manuals (and, for earlier 216s/235s?).