Anyone have experience with a 4bbl 450 CFM Holley Economaster Carb...

I think it depends on what it's on. Like on a slant 6 for example, it might work pretty good. I have a very complete one myself and I'm going to put a kit in it one of these days. Holley made several different Economaster carburetors. One barrel, two barrel and four barrel. There was a one barrel in the for sale section recently.