UPDATE:
I had the yokes welded. It turned out to be cast steel, so it was welded with MIG without issues. I had to grind the weld myself to fit the hole on the cap iron. Unfortunatelly, I have put the fork part of the yoke into the vice and closed it a little bit more, so one of the yokes broke apart. But the other welded piece worked just fine.
I have ordered a replacement brass yokes for Juuma planes from here
https://www.fine-tools.com/juumaplaneparts.html
They are very cheap so I took the risk without knowing if it would fit my 100 year old Stanley planes. I have bought new yokes for both my Stanley planes. And they fit exceptionally well. The yoke is now fully engaged in the slot of the cap iron and it has considerably less slack when turning the adjustment wheel. The only downside is that the pin that holds the yoke is a little bit loose, but not so loose that it would fall off randomly. In case it happens in the future, I still have original steel pins from the plane.