used copper head gaskets for many years with only the o-ring in the block. Main issue is do not have the o-ring too tall out of the block.
from SCE "Recommended o-ring protrusion is not more than 25% of gasket thickness (see figure 1 below). Wire height in excess of 25% gasket thickness without receiver grooves may cause coolant leaks by supporting the cylinder head too high for proper coolant sealing. Example: Gasket thickness .043”, o-ring protrusion height should be .008” to .010”. This standard works with all thicknesses that are .050” and less. Gaskets thicker than .050” do not require o-ring height more than .012”.

I find .010 the proper height. Then I use motoseal, around the water ports, it is a thin silicone sealant designed for metal to metal applications. works great.