I just dissembled a set of carbs today that had the gasket on the left as the center metering block gasket,owner told me it always was rich,leaking fuel and couldn't get idle below 1200 rpm. I've had more than one over the years that someone changed gaskets/rebuilt that had the 4160 4 bbl gasket instead of the correct 2300 gasket,easy mistake.

On another note,I finished my 4 spd bird in 1992,cam is old Direct Connection Street Hemi grind,280/474,end carbs have unmodified correct 34 and 35 metering plates and #.065 main jets,doesn't run rich,no black exhaust tips,about 17 mpg if you drive sensibly, runs like a clock, and hasn't been touched in 20 yrs.