The issue that arises is that almost all aluminum alloy tubed frames
are heat treated after assembly (welding).

This increases considerably their overall strength, but it makes
them, for all practical purposes, unweldable. The heat of welding
resets the area around the weld and unless you can retreat the
whole frame again in some kind of annealing oven, it will give
up pretty quickly somewhere near that spot.

Even putting some kind of sleeve over that part of your tube thus
becomes impossible.

When I was a glassblower, we used large annealing ovens that might
fit a bike frame, but you still end up with painting issues and I'm not
100% sure of the heat treating temps required for your particular
tubing.......or if it early enough in history, whether it was heat treated
at all.

I wouldn't personally ride it now. You might be able to sleeve the area
with some sort of cut to measure alloy sleeve attached with a cold
process.....like epoxy. If you try this (and I would advise against it),
make sure the sleeve is pretty snug and that you have removed the paint
and roughed the surface in the area of the sleeve.

Nothing is forever, my friend.