Another Question - C59A block coolant passage

[Ziggster]

I just noticed this threaded passage in the block just behind the water pump mating surface as I was prepping it for paint. In all the years I’ve now had this engine, I don’t think I ever noticed them. Going through the flathead books I have, I see no mention of them. The one book by Mike Bishop & Vern Tardel show a block being assembled with the port blocked off, while I. The book by Tony Thacker & Mike Hernan the block used in their assembly pics has no port. So, the question is what were these ports for? Will now need to get more 1/4” NPT brass plugs.