The meter block is different but I can’t tell you the difference. The emulsion tubes inside have different holes but you can’t get in there to measure them. Different cams have different vacuum so they all require tweaking some. Sometimes they interchange fine. The air bleeds may be different as well. I have never measured those.
Agreed,... also regarding the air bleeds, they are larger on the 340 carbs, also the #4790 340 (auto) center is 350 cfm, the #4791 340 (manual) center carb is 355 CFM
As far as the OP's question on using a 340 carb(s) on a 440, no problem, I actually prefer running the 340 carbs on B/RB applications, mostly for the larger air bleeds
Mike
