Best Solution for Control of Multiple Furnace/Heating System

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In 1993 I installed an old Simplex Multitherm as the primary heating system in my house. A hot water maker on a zone supplies the hot water. Burned wood mostly and had the oil burner as backup. Price of oil went way up so I stopped using the oil burner completely about 15 years ago. Oil burner needs a new transformer and regen tile but is so inefficient because of the bare convection tubes that it isn't worth using. Switched to coal about 10 years ago. Still used wood for hot water in the summer. Then added another hot water maker which can be used in series or parallel. Got married, have a new kid, got old, etc so on the way home from the hospital saw a domestic hot water furnace and a hot water furnace on the side of the road. Two years old and cheap. Bought them and installed them. Still want to heat primarily with coal in the winter.
Basis of the issue-
#1 The oil hot water heater supplies the domestic hot water in the summer. I am fine with that. I piped it up after the hot water makers so in the winter when I am burning coal the oil burner should not run as the feed to it will be hot. The problem is that I only want the circulators for the hot water makers to run when the coal furnace is hot.
#2 I switched the circulators over to a Taco SR506. It has an isolated end switch to the new oil fired boiler. I would like to break this with a switch that does let the oil furnace run if the coal furnace is up to temp.
Question is...-
How is it best to accomplish this.
!. I was thinking of using the Aquastat (L8124A,C) on the coal furnace by taking out the wires and using the low and high limit switches. I could run the end switch from the Taco to the R-B of the low limit (24VAC) and run the hot water maker power feed thru the R-B terminals of the Hi limit (110AC). Basically just use the switches. Not sure if I can just pull out the wires and add mine. Anyone tried this?
Note: There is another Aquastat switch on the boiler, L6006 I think that I use to dump heat to the cellar and garage if the coal furnace gets to hot. This is a 1975 furnace so I am leery of adding thermowells for additional controls.
Unfortunately I am an engineer so I want the system to do exactly what I want. Any suggestions how to accomplish this would be appreciated.
Regards
Al

Welcome.

Pass one leg of that end switch through a L4006A control. It will break on rise, set the temperature accordingly.

If you do not have a convenient place to install an aquastat well, you can get a version that straps on the pipe.

You have addressed half the issue if I add an Aquatstat. This is why I was thinking to use the switches of the L8124A,C if I can pull the wires out and use it this way. I currently am sending not thermostat or power to the Aquastat.
There has to be a simpler better way.
Al

If there is a L8124 on the coal boiler already, you can use the ZC terminal for circulator control. This terminal only has power if the low limit setting has been met.