I have used a Permaset Premium Grand Prix gasket on my old hump since 1997. The cross flows are 38 mm wider than the non-cross flows, so no US gasket fits...yet!
I'd go for copper, and use good preventative maintenance to ensure the galvanic action doesn't pit the cylinder head. Some of the rare US alloy blocked 225 Slant Six Chrylser engines used to corrode by pitting when copper was used.
The best one I've heard of is Araldite. If your headgasket develops a leak, you shouldn't have much problem removing it if you use a port-a power. Just a crazy thought... :!: Turbo guys in the States with Cosworth headed 2.5 (Pinto/Lima) OHC SVO four cylinder blocks have been doing it for years!
The Falcon six needs five bolts per cylinder like a Ch**y small block to keep the gasket stable. The Ford six has a stone cold number one cylinder with a water pump, and very little support on the true left-hand side of the block, even less than the pre cross flow 'cause the head bolts are that much further away.
I think there is heaps of thermal stress between an alloy head, cast iron block, and cold front end, hot back cylinders, and cool left hand side. All the exhast heat is on the right hand side, and I think that's what makes the block deck face buckle. You see it first on the propane fueled engines like mine, before you get it on turbos.
