There's an old carbon removal trick that I'll just mention (not necessarily recommend) that involves running the engine at around 1500-2000 RPM and dribbling a Coke bottle full of HOT water down the carburetor throat a little at a time. It supposedly steam-cleans carbon out of the combustion chambers. I've had mixed results with it, but engines I tore down after the procedure did have pretty clean combustion chambers.
If lifters were worn, there would have been corresponding wear on the camshaft lobes. Rig up a magnetic base dial indicator on the adjuster side of the rocker arms and compare cam lobe lift from one cylinder to another. Intake and exhaust lift numbers will probably be different, but all the intakes and all the exhausts should match closely with each other. If you're still running hydraulic lifters, it might be necessary to remove the rocker shaft assembly to get an accurate measurement of cam lift, since valve spring pressure could cause the lifters to leak down during the lift measurement process. When I was building race engines I had a pair of solid lifters with tall extensions for the dial indicator to contact when degreeing cams- - - -solid and hydraulic.
Jerry
