Is this it?



I'd make a flat reasonably heavy piece of strap steel and drill a hole in the end and bolt it to one of those flange bolts and hold it against the socket like a fulcrum and use either a breaker bar like 36" (pipe extender) or an impact gun. You in the air or on jack stands?
Maybe a helper on the strap and you on the nut?

Or bolt a piece of metal to the front of the flange that would interfere with a spot on the case to lock it while turning the flange nut?