Early years ('71-'75?) came from the factory with a cylinder base gasket. In later years, some owners installed a gasket to lower compression when pinging was a problem. Throw the old one away; they're aren't reusable.

Regardless of where it came from, if there's a base gasket installed, you must continue to use one. The cylinder wears, and a layer of carbon accumulates, at the upper travel limit of the piston ring. If you remove the base gasket, you lower this "ridge" and it may damage the piston when the upper ring collides with it.

Thin is high compression, thick is low compression. Replace with the correct version.

As with any part stamped from a sheet of metal, there is a sharp-edged side and a rounded-edged side. The sharp-edged side faces the engine case.