I think you're going overwhelm your 283. If I remember correctly, most original 283's came with about a 480 cfm four barrel carburetor....

You can use a formula to determine the CFM requirements for your engine. It's based upon the engine's cubic inches and the maximum RPMs that you expect to turn. You also need the VOLUMETRIC EFFICIENCY PERCENTAGE (VE%) of the engine. If an engine could use all of the air it ingested, it would have a VE% of 100%. Stock, production, low performance engines will fall around 75%-85% volumetric efficiency.

The formula is: CARB CFM = Cubic Inches x RPM's / 3,456 x VE%

So, if you can turn 5,250 RPM and your engine has a VE of 85%...

283 x 5,250 / 3,456 x 85% = 365 CFM

Dan J

And by the way, if you really have a "grocery getter", you don't want the mechanical secondaries with the double pumper. I'd suspect that you'd be better off with vacuum secondaries. Are you running an automatic transmission?