The bracket is ferrous, my guess is that it is forged steel. First thing you want to do is fabricate a jig to be able to position the shifter shaft properly BEFORE you do any grinding. Then your guy can grind the weld area flat and locate the center where the shaft will go. Drill the bracket to insert the shaft and weld. You will probably need to have a new shaft turned on a lathe, center drilled and threaded for the retaining bolt. Ask if you need dimensions on any of the parts.
edit: as SoakedKarma said earlier, you could use a bolt to replace the shaft - and a nut to hold the shifter on the bolt shaft
1985 Rebel 250 ... 2005 Ruckus 50
Keith from Maine USA - Banning Spammers since 2016