I can’t see exactly where the hole is, but it’s near impossible to fix an issue like that on cast iron. You can’t get enough materiel in the right place to make it solid. So basically you end up with a blob of weld over a thin spot.
There is a chance you can pin the thing IF there is enough metal there to hold the pins.
Don’t polish the chambers. You can use a 40 grit paper roll, but that’s as fine as I’d go.
