Scott, as you have noticed the early water pumps for the 216 (37-40) are different than the later 216 (41-53). Earlier pumps have one hole and the later two holes that connect with the water passage of the block. Since your engine overheats immediately I am wondering if a mismatch of pump to block may result in no flow at all. Before pulling the head why don't you pull the water pump just to be sure.
I found out about this when I ordered a new pump for my 37 and ended up having the original rebuilt. I confess I am not certain it matters but fairly easy to check before pulling the head.
Kent
