Early head gaskets were multi piece. The "gasket" was merely a sheet of, I think, some sort of fiber laminated in something to make it hard, kinda like fiber glass. The fire rings were loose in the package. You put the fire rings around the liner and installed the gasket, or shim really, this allowed the fire ring to compress but not so much that the head, when torqued, would contact the top of the liner. There were no water/oil passage grommets or seals, just holes in the shim at the passages. There was a split in the gasket that aligned with the exhaust port so that in the case of a hydrolock situation, the liquid would push out the groove and save a bent rod, in theory. If the fire ring blew, the teltale sign would be an exhaust leak at that point and it made a loud ticking noise. You can ID an old style gasket by a tab sticking out between the head and deck under the exh. port
I personally know people that thought the exh manifold gaskets were leaking, pulled all that stuff off, remember, the intake and exhaust are on the same side all intertwined around each other, replaced the gaskets and had the same noise after assembly.
New, modern gaskets look like any other SB Chevy. water and oil passage inserts, fire ring made with the gasket.
If it were me, I would run it until it left a puddle after you park it or popped a fire ring out, but the later can cause damage to the liner, head and deck, then the repair gets complicated and expensive. The job isn't bad, I thought it was easy and fun to do, probably because it was MUCH simpler than the stuff I was working on daily. When you go there plan on other things, oil cooler hoses, the water rail hoses, turbo drain hose, probably renew the return and flame heater lines.
IIRC, the oil passages are front and rear, push rod side. It is also common for the oil leak to be at the rear of the block/head, between the heads and at the front. the closest points to the oil passage.
The image below of the NEW gasket is actually of a newer gasket, but not the latest. The latest has seal beads around all of the oil and coolant passages and I think, around the perimeter of the gasket. I just was lazy and didn't look too hard for images!
