I've had mixed results with a mig welder... also used another junk sieve and put two together.
I'm thinking someone could make a little money making new sieves for some old collector combines. You can buy new aftermarket stuff. It would not take a whole lot to customize a size.
I have a suspicion that Deere and maybe others are playing games with some of the older stuff. Last year, I went looking for a sieve for our 105, and checked with 3 aftermarket suppliers. All seemed ver anxious to help, but upon checking their notes, "no, we CAN"T do that". Some of these companies had sieves and chaffers only a year or to earlier! The insistance that nothing could be done, and the hurry to get off the phone made me wonder if Deere said, "we don't wan't to support this old stuff any more, and niether should you."
Something was definitely up.
Anyway, good luck. You may consider measuring what you have, and find if anything currently available might fit. I learned that a 1460 IH chaffer was the right length and 1 1/4 in narrower than a 105 chaffer...