The Reset handles look similar to those used on Type XO frames, and the era is about right for the installation of XO equipment...
The frames do not line up next to each other - and there's "Odd / Even" circuit spacing ("Left / Right"), plus a very wide space between the "Left / Right" handles, which makes me think this is something in the "A1" or type "A Block" Family.
The typical XO Bus kits I have seen (1Ø 120/240 VAC, 100 Amps Max. common Residential usage) look much like an old Zinsco Bus kit for Plug-On type "Q" frames. The Bus Bars run the length of the Bus Kit, and Breaker frames are plugged in "one behind the other" - in a single row fashion.
The Plug-On Termination clips, for the Line side connection of the C/B frame to a certain Bus Bar, can be repositioned to land on "The Closer" or "The Farther" Bus bar. This is regarding 1 Pole Frames. 2 Pole Frames have one Pole's clip set for the closer Bus, and the other Pole's clip set for the farther Bus.
(it's been awhile since I last seen XO equipment, so I may be a little off... or way off!).
The Panelboard in the Images appears (to me) like it has the "A-Block" Modular equipment (maybe that is "M-Block"???)
Again, I cannot remember the Sq. D Model of those things - they are similar to the Modular Kits made by G.E. - under the Trumbull name ("The Trumbull Electric Mfg. Co." - A General Electric Organization).
Would be nice to know what the equipment type actually is in the image...
Time to go dig up some Antique Square D Panelboards!
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!