Hate to say it but the 235 I have apart right now has the same coolant hole situation. It hasn't been apart in decades.
There is a small hole in the head opposite the blank spots on the block. I was sorely tempted to drill the block.
I did find that some of the smaller holes in the block and head were packed full of rust scale that had gotten caught and accumulated there. That would be more than enough to restrict flow and cause it to run hot.
I did remove freeze plugs and use a pressure washer to clean out the block. Have it on an engine stand so I could rotate it upside down and sideways. Got a fair amount of crap out but there wasn't as much as I had expected. The head seemed to have more scale than the block.
