I'm really interessted as well. My antifreeze is quite rust- contaminated and flushing with water just won't clear it properly. Are there any risks involved in using a coolant flush in an 40 year old engine (lehman 120)?
I Flushed my system with Oxalik acid and vinegar and ran my engine for an hour, next I ran a mix of baking soda and water and ran that for 1/2 an hour then did two fresh water flushes. I never got any sludge but did get a lot of brown water.