Back 60 years ago, when I was just getting into vehicles and maintenance,there was a 2 part flush that came in a tall cardboard container as I remember and I think it was a Dupont product. You would dump the cleaner part into a warm engine and run it for quite a while, then drain it and flush with fresh water and drain again and then fill with the neutralizer portion of the product in it and run it for quite awhile again before draining and flushing again. If my feeble memory serves me right I believe that at some point the thermostat had to be removed and the heater had to be run on high while all this was going on. Then, after flushing well again, you drained it and re installed the thermostat and filled the system with a 50/50 mix of water and antifreeze.You had to run it enough to warm it up well and make sure all the air was bled out and top it off again, a real pita.I do remember that some of those old cars had really filthy cooling systems and as often as not you would end up taking the radiator off and having it rodded out.
The most recent experience I had with cooling system problems was with a boat I had that had twin 3208 Cat engines that were fresh water cooled with a raw water heat exchanger.I did some pretty extensive work on the boat including the cooling systems and at that time Cat recommended using de ionized water with the anti freeze mix.
There are a lot of different thoughts on this subject, especially with the newer stuff with so many different alloys.