Chris definitely a mismatch with that new water pump pulley. Actually looks to be a 5/8" wide piece, which is a common size for the early engines. The majority of flaps just take the rebuilders word for what the pump fits, with no real attempt to accurately match the pump casting and/or pulley.
We as buyers are stuck with trying to coerce them into finding the right parts to match the item it's replacing, usually requiring visual side by side comparison. Your old pump pulley may seem likes its stuck and unmovable, but I'm confident you can encourage it to release from the pump hub and transfer it to your new pump.
