Help Stoker-man, I need a measurement

Stokerman (or anyone else with a new efm 520 boiler), can you measure the space between the water jackets behind the baffles please? I would like to clean my boiler without buying the online only horseshoe shaped brush plus shipping, so if I know what size round brush to use I can just get one from the hardware store for $8. I would like to shut down just long enough to clean the unit but not so long as to have the water cool off.

Ed. A 2" Round Noodel brush with a 3 ft Handel The Space Between the Heat Exchangers Ar 1 3/4 " From the back to the front Door is 3 ft Take the two baffel plates out and go threw there