Thanks for the burping advice.
So I finally got around to pulling the heat exchanger. Overall, I would say it is pretty good shape. I found a local radiator shop and I am going to have it pressure tested and cleaned. I am also going to replace the gasket and add a lock washer.
Upon inspection, it appeared that the zinc hole was plugged and the rumored brass plug was missing. I assumed that an old zinc was lodged in the hole. I used an awl to scratch the metal and it appears to be copper! The part is a Sen-Dure 2737 (also 298633). The threads where the brass plug portion of the zinc appear to be missing or in rough shape. Could the use of a zinc have been optional where the installer/user would have to drill the hole?
If this is the case I am guessing I can ignore the zinc on this heat exchanger and reinstall assuming a clean bill of health from the pressure testing/cleaning? Thoughts? Photos below: