There has been several long and detailed threads on headgaskets and how to make them, but I think in the middle of making a better gasket we found out why the old ones blow. I have a STACK of blown ones!
Here's what we found-- The cylinder liner protrusion must NOT be more than .010" above the deck. Five to seven thou is pefect, some are more than .040! A little protrusion gives the different rates of expansion of the liner and block to 'catch up' with each other. Mine is currently running at .004 protrusion flawlessly. If it's too 'tall' the head bolts are pulling the head down like a skull cap.
I still think the only time my Listers have ever REALLY scared me was one cold morning winding up the crank handle with a snort of starting fluid in the intake and when I dumped the lifter the head gasket blew a spitball of semi-frozen gasket goo directly in my left ear.
The OEM gaskets have a powder dry artificial (I hope) asbestos felt between two sheets of copper. This liner absorbs some water and can leak. The solution seems to be to thin gasket shellac , available at the auto parts store, with denatured alcohol about one part goo to ten parts solvent and stir it up with a little acid brush or dauber and really soak that liner. Paint it on both sides and bend the copper back carefully to get some liquid on all sides of all the holes. By the time you're finished with this job anything you touch goes with you...that shellac stuff is STICKY. Wipe both sides of the gasket with alcohol to remove fingerprints and excess goo. Spray paint the gasket with alumimum paint and let it dry, but only about half hour. Dry the paint but not the goo inside.
I torqued the head down two grunts tight six months and 2300 hours ago with absolutely no leaks and no problems.
It's customary to re-use headgaskets unless they're blown on Listers. NEVER thow one away! You can run a Lister with a circle of copper wire strung around the fire ring of the blown gasket in a pinch.