Take the oil cap off whilst the engines running and it should stall - i.e. its breathing ok (although idle may have been wound up a bit if its cam'ed, so it might not stall but should slow the engine speed). Check cap for head gasket signs of mayonise whilst its in your hands. Idle should be around 950-1000 rpm.

Might sound tappety - which is probably worn tappets (easy fix) but older engines it prob indicates worn cam. If uprated cam is in there then it could just be noiser in the head anyway, and particularly if theres uprated valve gears, double springs etc.