if they still have a half round of original hole get some u-bolt washers there thick and beefy . set them up in place and line up the half hold and washer hole and weld them up .
this is would be a lot less work in the end . and who wants to mess with rivets . . . . unless your fully setup fr that stuff.
I prefer to keep rivets if possible. but if I do have to nut/bolt 7/16 bolt and open the hole a tiny bit for them and get a bolt with a shoulder and use stover nuts ( metal crimp lock nuts )