My apologies if I've missed my suggestion in any of the other replies -
You say the water pump was good on your 216 (year?) and that this is a '53 235. There were at least two different pumps that mounted in front of the block and head on various stovebolts, with variations of seals, bearings etc within the types. Early 216 (and maybe some very early 235?) had a backing plate on the pump that had one hole. Later 216 (1942 onward?) and most 235 had a backing plate with two holes. Naturally, it's not as simple as just changing the plates as the holes in block and pump won't line up and the pump castings are shaped to direct the flow to the holes in the backing plate. If you find this is the problem, the good news is that the 2 hole pumps are readily available (Rockauto lists 3 price-points for the '53 235) while the one hole pumps seem to be a "rebuild your pump" at most suppliers.
