You're on the right track, you need to start with the basics first. Holden six harmonic balancers are well known to spin the outer ring with great regularity. Any sideways wobble while it is idling then to me it is sus. As far as the rest goes if that means pulling the harmonic balancer and timing cover to check the cam timing (you may as well throw a degree wheel and dial gauge on it while you're there if this thing is really that much of an unknown unless you can find some reliable data on the cam) then at least if you start from the beginning to both: A. Work out what you've got, and B. Give you a reference line from which to start (ie; if the cam needs to be advanced or retarded from where it is).
Trust nothing you're told and only what you can verify yourself when taking on someone else's problem child. Have a good look at other base line items as well: wet and dry compression test, manifold gaskets, carby base gasket, vac lines, distributor set-up etc.
Bookmarks