390 FE Carburetor Size

[Falcon67]

I would like to try two of them on a tunnel ram, personally. 

[Riderjeff]

Carb threads are like oil threads... 

Summit sells a self-branded carb that's an update on the original Autolite 4100/Holley 84010, available in 600 and 750 cfm versions.  I suspect either of them would work well for the OP. Not too pricey, either!

[Heo]

I helped a kid rebuild a CSB a few months ago.  he put on
a Edelbrock 1407 he had. Young as he is he installed a lambda
on it and it has perfect fuel curve. Lambda 1.0 from idle to full
rpm

[Falcon67]

Carb threads are like oil threads... 

Summit sells a self-branded carb that's an update on the original Autolite 4100/Holley 84010, available in 600 and 750 cfm versions.  I suspect either of them would work well for the OP. Not too pricey, either!

Those are actually the obsolete/retired Holley 4010/4011 series carbs.  The work very well, use standard Holley parts and use annular boosters in the style of the old Ford 4100s.  I have an 84011 sitting on the shelf - 750 VS type.  I ran it on a street 351C 4V with 3.7 gears and a big single plane intake with a 2200 stall 11" converter.  Drove great and ran 8.40s in the 1/8 on street tires.  Holley dropped the line years ago, I imagine because they didn't sell very well since "That ain't no Holley carb".  Summit picked them up for some reason, I wonder if Holley is the OEM since they had the tooling.  Summit can likely move more of them since it's now a "Summit" carb and not pretending to be a Holley.