I separated the manifold from the riser and now need to replace the gasket. I noticed that there is a metal gasket the has all holes blocked but has one small bb size opening and a regular gasket with all 3 holes open. Is this normal?
Need more info.
The small bb sized opening in the elbow gaskets suggests Raw Water cooled, or at minimum, a "half "closed cooling system.
If the elbows are being fed sea water independantly of the manifolds, then the OEM gaskets are required.
Conversely, if the elbows are being fed sea water via the manifold "transfer ports", then the gaskets will need to be fully open for each transfer port.
I am replacing heads that were cracked due to overheating and broken head gasket.
Learn which pistons were used in this 1979 engine, and be sure that you replace the cylinder heads with like combustion chamber volume.
Back in 1979, these may very well be F/T pistons with the 76cc chambers.
Many of the later chambers are only 64cc, and were commonly used the full dished pistons.
The wrong combination (either way) will give you troubles.