Your 273 by the math, and assuming a VE of 70%,which is probably overly generous a VE; wants
(273 x3600)/3450 x 70%= 199cfm @3600rpm,
at 4000 maybe 222 cfm....
at 4500=249cfm.
If your engine is physically capable of pulling in only 249 cfm, there is no point in installing anything bigger. especially if it costs you money to install it..
However 2bbl carbs are rated different from 4bbl carbs, but in this instance I think it's nearly moot.
I had a 340 2bbl once; with a teener carb,,intake, heads, and cam, awesome lil combo in an early-A wagon.
If you do this swap, make sure you do some before and after time trials, to see what it was worth.
You'll have waaay better results with a higher stall TC and/or bigger rear gears.