Advice needed - Changing a vintage ceiling box to modern

[Citation]

Sigh... once again my wife wants to live in a vintage house but is frustrated because modern hardware seems to forgotten to work with 1930s wiring.

So my wife wants to change the dining room light fixture (again). The one she likes only works with a 3.5" screw spacing. Our vintage ceiling boxes just aren't that big. What reasonable options exist for replacing vintage wall boxes. Ideally I would like to deal with the wiring as well, perhaps trimming back the vintage stuff and using modern wiring where the connections are made so in a few years we can change the fixture again (sigh).

I guess there are two questions here.
1. What is the easiest, safe way to change out the existing ceiling box for a new one given the plaster ceiling and my generally poor skills with drywall much less plaster repair.

2. Is there a good way to splice into the vintage wiring outside of the new box that is still safe? I'm not sure if I would be able to install a second box inside of the ceiling. If I can that seems like a good option. If I make the attachment inside the new box is there an acceptable way to fix the vintage wires in place so they don't move as the new wires get tugged on during service. BTW, I think much of the old wiring was carried in armored housings that may or may not be grounded.

Thanks.

Edit: Just verified the wires in (and out) of this box are in armored housings. Also we won't be installing anything heavy like a ceiling fan on this box but I would be open to a ceiling fan mounting setup if that works well.

 

[Zeke]

 

[Citation]

That might work. Here is my current setup.

 

[Norcal]

It's CYA for the lighting fixture manufacturers but most spec 90°C supply wiring, the old wiring may not even have a 60°C rating. The existing box looks like a ****** off a hickey in the center, there is hardware to support a fixture off that, finding it may be more "fun".

 

[driftpin]

I suspect your insulation on that ancient wire is already riddled with cracks, and any tension on it, will cause failures of the crumbling insulation. I had work like that in a near 100 year-old house in FL (1926) that had a 60 amp branch circuit panel with 4 Edison-base fuses, and a separate pair of cartridge fuse boxes for the water heater and the stove.

Some of it I abandoned in-place, much of it was removed/replaced, I felt much better with everything new from the weatherhead through the meter can and main disconnect, to a 200 amp branch circuit panel, and all its branch circuits. I did everything except the disconnect/reconnect.

 

[CoogarXR]

I suspect your insulation on that ancient wire is already riddled with cracks,

It's woven fabric insulation. It doesn't crack.

 

[Bert_]

It's woven fabric insulation. It doesn't crack.

It's rubber underneath the woven layer. It definitely drys out and cracks. Especially in ceiling boxes.

If the insulation is crumbly you can slip some heat shrink over it. The problem is usually only in the box. Often the insulation is like brand new back in the sheath