Pin hole in cast iron head

So the short side of your heads is just JB between port and water passages ?

No, Just ground thru where the pushrod used to be. I grind the wall back so the pushrod bump is gone in the port. Then duct tape the inside of the port, stand it up, and fill the back side in with JB Weld. Since it's thicker on the outside of the head than the slot in the port the epoxy is in a wedge shape that vacuum is pulling against. You have gasoline on one side and hot oil on the other side. I've never had any sealing issues with this process.

My point to all of this was JB Weld does a really fine job without issue, so if there are even better products to be had you'll have great success using an epoxy.

That said, If I can get to it with a MIG or a TIG for that hole in the OP's port, welding would be my first choice, but if the OP doesn't have that option available just epoxy it.

Tom