Great additional information.
I agree that the water jacket in these stovebolt blocks can get pretty cruded up. I cannot believe how much gunk I flushed out of the block in my ‘37 Master coupe. We can only assume they cleaned the truck block decently when it was rebuilt. Except I am leery of assumptions like that.
Once upon a time the chemicals used when "hot tanking" a block might have removed the junk in the water jackets. For a few decades, at least in California, all it really does is de-grease the blocks. I spent an inordinate amount of time poking around with a stiff wire at the back of my block clearing out the very hard black chunks of gunk. I think the shortcut of adding lots of radiator stop leak rather than fixing radiators contribute to this problem
