wacw, I'd go with the Holley 390. You've got the 4BBL intake, why put a 2BBL carb on it??
I've recently upgraded from a 350 Holley on a 2BBL intake to a 390 on 4BBL. As long as I'm just cruising around the 390 gets better fuel economy, but of coarse that all goes south when all 4 barrels are opened up
Even with the secondarys "locked" shut with the heavy black spring and using it as a 2BBL carb while tuning the primarys, the responsiveness of the 390 is a lot better than the 350.
I know my engine is a different build to yours, I just thought I'd share my experiences of these 2 carbs. Don't get me wrong, I still think the 350 Holley is a great carb for a Slant 6 (my old Val ran mid 15sec 1/4 miles with the 350) I just think the 390 works better for my setup.
