64 Skylark 300 head gasket problem.

[BuickBoz]

I have a 64 Skylark 300. Previous owner replace the aluminum heads with cast iron. I had to remove the head to remove a broken exhaust manifld bolt. When I reinstalled the head with a new head gasket, etc. I have a coolant leak coming from the bottom of the gasket next to the oil stick hole (driver side)in the block. The head gasket covers a port on this area of the head but there is no mating surface on the block to compress and seal the gasket against the head. On the passenger side of the block there is a mating surface to the head.

Don't know how it was sealed before I removed it. Thinking to just tap and plug this port that goes nowhere.

Anyone one have info on this problem?