GMC Sierra 1500 '87, Goodwrench 350 '07, Muncie '13.

I have a weird not-so-disturbing issue with my Goodwrench 350. 10 years and 50000 miles on it. Easy driving 5000 miles/year.
It'* an excellent engine, fires up immediately every time, runs smoothly on the road, but cylinder #2 seems to misfire at idle. I suspect #2 because of different color of header tube.
Also the right side exhaust puffs smoke rings in wintertime (at idle), which I think is due to unburned fuel lighting up in the exhaust pipe. CH and CO emissions are also bad on the right side pipe.
I can get acceptable figures by adjusting the Holley "out-of-balance" that is turning the right side mixture screw down to ¼ - ½ turns open, leaving the left side at 1½ open.
Idle vacuum is 18-19 psi at normal temp. No oil loss between changes (twice annually)
Compression ok, blow-by ok (12% I recall), spark plugs ok. Since it don't have no affection on my everyday driving, I have not really done nothing about it, except tunin the carb before emission tests.
Somewhere I read about wrong length push rods mistakingly ending up in engines.
Is this possible and what would this cause? Too long/too short, intake/exhaust?
How can I determine correct push rod length without taking the engine totally to pieces?

Remove both valve covers, measure the rocker arm travel on one side vs the other side. This will tell you if the push rods are different length.