I have several "parts" H-4's, and would sell you an 6515DAX "mounting flange" for $5 plus shipping.
email if interested, firstname.lastname@example.org
If you are going to get that deep into the mag, you need the "Blue Ribbon Service Manual, GSS-5035.
You can view it and print the pages you need at the link below. You will have to copy the link, and paste it into the address bar of your browser, as it doesn't work to post it here as a clickable link.