Mine is different. No bolts, just a crimped rim. Probably not original to the truck but stuck on afterwards.
I talked with my International Harvester navistar parts guy and he said bring it up and maybe he could match up something.
In the meantime I have my trucks rear in perpetual high range and its decently roadable.
If I find a compatible vacuum shifting unit I`ll post the part numbers so it may help others.
Thanks to all
John