How to hang modern fixture over old square recessed box?
If that was installed in 1958, the wire may or may not have PVC insulation. If it's the old rubber insulation, it's going to be brittle. Bending the wires could crack and compromise the insulation.

Also, it's virtually guaranteed that there is no ground wire in that fixture. You should check local electrical code to make sure that replacing the fixture doesn't require you to bring the whole circuit up to code with new wire. If it does, code requires a grounding wire everywhere, every metal fixture must be grounded, and you'll have to have a neutral in the switch box.

Personally, I would be looking to pull new wire to that spot, rip and replace the ceiling box, and enjoy the confidence that I didn't create a fire or electrocution hazard. That is unless I could inspect the existing wire and the underlying box without damaging it, and gain an assurance that the existing wire will be safe and will reach appropriately into the new ceiling box. You can't make splices inside walls. If the wires aren't long enough, they have to be spliced in a junction box. (There are devices for splicing NM cable inside walls, but I doubt they're approved for use with 60 year old wire that isn't constructed with modern materials).