Good compression, plus fouled plugs on only one side screams "Vacuum Leak"! A milled head can expose the bottom of the intake passageways to the crankcase unless the intake is also milled to align the ports, and it ALWAYS happens on the bottom. Some NASCAR teams did that deliberately. The engine would run lousy and smoke during caution laps, then clear out and suck a little extra air past the restrictor plate at speed. One backfire can push the bottom of the intake gasket out and create a vacuum leak on an otherwise good-running engine if the gasket is just barely sealing before.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!