I am curious what about this adapter plate makes the cooling better? Is the the fact you are moving the pump to the middle of the radiator or is the older pump a better design? It seems like the adapter plate would pull the impeller out of the existing 4" hole in the block and make is harder to pump the coolant.
Pumping more GPM doesn't necessarily mean it will cool better. Slower moving coolant allows more time for engine to transfer more heat to the coolant, then for the coolant to transfer more heat to the radiator. In addition, for those that are replacing their 216 and early 235's with later model 235-261's, the longer pump interferes with the radiator. You can resolved this issue by buying a short shaft water pump made specifically for this mod, shorting the pump yourself, or moving the radiator to the front of the support. None of these mods will center the pump on the radiator causing inefficient cooling. Some 'bolters have done this and attest to no cooling issues, but others have not been as lucky.
I have installed this adaptor on a '59 235 in my '52 Chevy 3100 and it works great.
My hats off to "Pre '68 Dave".
