(Sting wrote ) Other examples can be found in all that drivel I used to spew regarding System Balance.[/quote]
Sting , you have opened my eyes many times. ( love some of your avitars
) I grew up fixing all things that go fast and never had experience with heating.
As you said , to hack , adapt, or add a coal boiler into an existing system can be a challenge. I agree with the reasons for " pumping away " and only add this post for some other guy who faces a challenge of space being practical only on return for his pumps.
I have an old two loop mono-flow system than gave yearly air bound troubles. She was fired by an oil burner.
I read 3 times, Stings posts about mono-flow and balance and decided to keep the system while replacing the oil boiler with a coal fired one. My buddy Rich and I re-piped most of the copper surrounding the boiler and because of very little clearance we gave into mounting the two pumps on the returns up by the floor joist.
We have lived here 30 years, this is the first year with great heat, plenty of DHW, and no issues. I only air bleed the system on install.
So from my very limited experience I say, do the best you can and don't sweat what is the unachievable,the quest for perfection.
Many Thanks Sting ! And all for lending your help.