I agree, running only #3 as the primary (out of 3 on line, 2 dead holes) is going to favor the center port.
I haven't examined a Howard myself, but based on the descriptions and photographs there was no serious attempt to equalize mixture distribution in most multi-carb log manifolda. The manifolds were basically just plumbing fittings, with constant ID, no taper, and no internal dams etc. to bias fuel flow. Aftermarket manifolds were, IMHO, pretty crude with improved WOT power as the only target until perhaps 1960. There was no commercial attempt to use plenum volume until the SBC injected motor in 1957, and the Ridgerunner (1962?), and no tuned lengths until the B & RB Commandos in 1960 and the Hyper-Pak. Even the factory stuff needed some help - Chrysler published many diagrams on how to re-dedicate mixture flow in the manifolds.
Using # 2 & 4 is going to be closer to what you want for normal use, and progressive (staged) carbs even better.
