One thing to keep in mind is that they have an early '69 pump and a '69.5 and up pump.

The early is 4 & 3/32" from the snout to the top of the pump. The late one is 4 & 9/32" from the snout to the top of the pump. I don't know which pulley/component causes the problem but you'll have an alignment issue if you try to mix long-short snout pumps.