Trying to figure out AFR reading

Yeah the chart assumes you are running petrol with no ethanol in it

i'd concentrate on moving idle up to average of about 13.7
aiming for 14 when i lift off the gas at speed
worry about the top end when you get the bottom end done

The stoichiometric number for e10 10% ethanol fuel is 14 to 14.1 and non ethanol fuel should be 14.7

mismatch between plugs is more likely distribution or ignition. if you have flat spots you will be leaving unburnt fuel to gum up your plugs

you might need your idle mix screws turned in or out so they don't match side for side depends on the carb and plenum size, how tall the carb mounting flange is and the firing order

the holes that the idle mixture comes out of favour the cylinders that draw it more directly
if it has to do a 180 turn it will be differently mixed and atomised so there will always be some mismatch, can't say if that is going to make a cylinder rich or lean because that is down to how well it burns as well as how much is delivered and how finely graded the fuel is in the air .