I am installing dual Carter B&B carbs on my basically stock 218 six with Offy manifold and cast iron headers. I recently was told this set up will not work, though a lot of guys run it. Its too much carburetion (two much air volume) and will cause poor low end performance. Is this what others have experienced? and is there anything I can do to improve this set up? Thx

How large are the carburetors?

The bore is 1 1/2" and the venturi is 1 1/4"

Yes, that's quite a jump up, and will have idle tip-in and response problems.
What sort of power system do they have?

Ball & Ball carbs have a mechanical accelerator pump that is adjustable based on where a pull rod is attached (controlling the length of travel - pump stroke). This is good for a dual carb setup because it doesn't depend on vacuum.

But to panic's point about a jump: Hollander Interchange shows the original equipment to be a number 11 flange:

Hollander number 11E - which is a Stromberg EXV-2 which has a 1.25" flange. Your 1.5" flange is Hollander number 21 - used on Dodge trucks (21W). Just one is a 44% increase in throttle area:
flange . . . . .radius . . . .r2 . . . . . .area
1.25 . . . . . .0.625 . . . . 0.390625 . . 1.22718463 +44% throttle area
1.5 . . . . . . 0.75 . . . . . 0.5625 . . . . 1.767145868 +0.539961237 sq inch delta

There was also 1 3/8" flange B&B used on Desoto - but that is still 21% increase in just one carb.

When going to a dual one needs to fit carbs that are smaller then the original . . . and/or make engine mods that increase the CFM demands over stock specs.

Thanks for the quick replies. Looks like these carbs just aren't going to work without some major engine modifications.

What's the manifold's bolt flange width?
The smaller engines need the #2 (2-11/16”) SAE flange for a bolt-on small carburetor.
The Rochester Model "B" from a Gen-3 (later) 194" L6 looks pretty good, 1-1/2" throttle disc with much smaller 1-1/16" venturi.

These are D6H2's with larger 2 15/16" bolt pattern.

There's probably a #2 to #3 adapter, but that will add some height. Re-drilling the manifold will be tough, I would begin by threading 5/16" aluminum rod to 5/16-18NC and bottoming them in the holes with epoxy, saw off flush, then drill & tap the new (closer) holes partially in the rod insert.
I don't see anything small enough to work well without mods, and still fit your flange pattern.
Some Zeniths may fit and have interchangeable venturis, but IDK much about them.

Considering any other work on the engine?

Of course, what you really need is a 25" Chrysler 265 engine (no, it's not a direct bolt-in).

Thanks, Panic, for your suggestions and advice. I should have done more mods to the engine when I rebuilt it. The engine is rebuilt to stock specs so probably won't dig into it again anytime soon.
I understand I can do something with small Holley Weber 2bbl carbs from an 80's Ford Fiesta, with adapters, etc. but I don't think it would have the old school look I want. Looking like I will go back to the original single carb and exhaust and move on to another project. Thx to all who replied.