My '52 216 used a 5/8" belt. I converted to 12v alternator and switched to a 3/8" belt. The 53 216 used 3/8" belt and hence water pump. I had a dual groove dampener made to accept the 3/8" belt. Much easier to find accessories with 3/8" pulleys than the old 5/8" belts.
So, water pumps for the 216 can be had in either 3/8" or 5/8". Since, you are already using the 216 pump on the 235.
