This may be a little unconventional, but I filed the hole left by the broken frankinpin square, then put in an apropriate length 5/16 carrage bolt and tightened the nut on the inside of the magazine box. If nessesary, I can weld the nut to the bolt to make it permenent. Then I blued the outside and the result is, you barely notice it.
It's a different approach, but it's simple, and it works.



























