"there are many other tuning factors." Very true- timing is just one part of the total tuning package.
How does it run? Any pinging? It may be set up just fine for your engine. Good gas mileage? Maybe just leave it alone.
Is it a Mallory dual point distributor? Or a Unilite? I prefer a GM Pontiac HEI distributor w/vacuum advance but I always use low compression heads. It takes very little adjustment to get it dialed in. Low compression lets me use lots of timing advance.
Stock 1968 heads are usually high compression and that causes all sorts of issues with today's crummy gas. Often, hooking the vacuum advance up to full manifold vacuum helps a lot.
