elcetricity question

There is only one safe way that I see and that would be to add another modern panel and tap into the hard lines coming in. That way you would have a main breaker and another breaker big enough to handle the draw for the welder, essentially bypassing that particular box and those screw in fuses just for the welder and maybe a couple of outlets if you wanted them.

How far is that panel from your garage if you have one.