The L6 valve cover was common all the way up to the 292s. The grommet [~1-1/8" , cup shaped] the dealer sells for the side air cleaner/oil breather is usually solid and has to be cut open to use the air breather. Don't cut it and there's your plug. May be available at Checker / Autozone etc, too.
I/I #4101
'71 GMC Jimmy 350, sm465, np205,3.73 posi.
'68 C/10 Stepside 292 (.030 over) Offy Intake, 500 CFM AFB,Clif headers, sm465, 3.73 posi.
'67 K/10 454 project.
'72 K/5 rolling frame project.
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