Spanky,
I don't know if this will help you or not. Back when I first got the 450 I was having intermittent fuel problems. I thought it was the fuel pump, and tracked down one. This was before you alerted me to the "stacked washer" fuel filter at the carb inlet. That turned out to be where my problem was so i never installed the pump, so this may or may not be correct for your application, or mine either. The pump I have is a non-vacuum assist model. It is a Carquest part number 531. It passed the "eye ball" test, but I don't know that it will actually fit. My parts guy used the GM numbers and some casting numbers I read off the pump to come up with that number.
Hope that is of some help,
Scott
