Something I would recommend to all members doing valve lash adjustments, is to unscrew/remove the tappet adjuster before setting the lash (takes only a moment) and inspect the tip for cracks, broken-off chunks, and wear. Given the age, previous owner neglect, improper oil, and just plain history, these tappet adjusters can be wornout and/or needing replacement. The tappet ends were hardened at the factory, and relied on the zddp additive of the day to cushion them. There is a service on eBay that will regrind, not sure if they harden them. A skillful home machinist can regrind and case-harden. All my tappet adjusters were chipped, made noise, and were reground/hardened, noise reduced to normal.
