I found the same problem of "It ran ok at lower speeds but never performed well at wide open throttle despite jetting changes" myself with both the two bbl or a 4 bbl on a Offy manifold.
I went to a 2x1 and bingo things went a whole lot better. I believe that it has more to do with even distrubution of the gases from the carbs to the intake on the head. With a carb only in the middle, high rpm's will vaporize the fuel real good but at low rpm's it has a tendency to "puddle". If you reverse to set up to get it to run good at low rpm's them it don't want to run worth a crap at high rpm's. Where as a 2x1 with the correct carb's will do both because the carbs are more equal distance to all the head intake ports. (the raw gas has more equal time to vaproize before reaching the intake valves) and that way all 6 cyl. are more ballanced.
My $.02 (for a daily driver)
