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What size engine are you working on??

I checked my stock lower pulleys from the 72 402. I have 2 of them kicking around here, (one I got from a dealer when I built an older Monte, different part numbers, but same pulley dimensions). Both are the same 7 11/16" as you have. The water pump pulley that was on the car originally is 6 3/16" diameter and has a GM part # 3995631AO. At least on my car, those are the stock pulleys used on a BB A/C engine. What diameter is your WP pulley? The WP pulley listed above seems to fit both small & big blocks.