Original panel dates to 1957. No issues with it but I've read about the many bad things about this unit. Also, the local codes now require 100A service and the present panel with two mains of 30 for the dryer circuit and 50 for the rest of the panel is now obsolete.
So the question is whether anyone is offering replacement internal guts for this unit. It's model 116-68C. If so I think I'd go that route.
Old box is flush in the wall.
If an entirely new box is needed, could one remove the existing guts and leave the old box in place? Mount a new panel right inside the old and maybe use the old cover, cut a big rectangle out leaving just a sort of rectangular ring and place it so as to cover the area where wires are emerging from their conduits (formerly the interor of the old box) and going an inch or so to enter the new box.
OR
What if one got a new box that was intentially larger than the old and mounted it on the surface in front of the old box? Again, the old box would be stripped of guts, and the cover removed and the box left in the wall. Wires could enter the new box from the rear. Those existing wires able to reach a breaker could go directly in. Those too short would just have new, longer runs pulled from their first place they go to (outlet box typically).