Rocketman,
I do not think welding on any pressure-bearing part of a firearm is a good idea since the high temps effects the characteristics of the metal. While it may have originally been manufactured using a welding process, the manufacturer had (even in Universal's case) some form of metal tempering and quality control to ensure the end product was safe.

The availability of spare parts for the later generations of Universals is zero and usually comes only with the salvaging of parts from another Universal. My advice to you is to actually strip the universal and part it out. Someone else looking for a slide, trigger housing, bolt, etc would undoubtedly pay cash. The sum of the parts you sell will pass the value of the weapon as a whole. When you are done, you can put the cash towards another carbine (either post-war commercial or USGI).

I own one but have it shoved in the back of the safe for several reasons - one of which is I know that I can not find spare parts for it if something breaks.

Just my two cents worth...