I didn't know you could use an earlier 216 water pump in a later 235 (without Pre'68 Dave's adaptor plate). I thought you had to use a 235 pump which puts the impellar inside the block, either as a short shaft modification or moving the radiator. Could this be your problem?
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix