I think you've hit the right idea, but how about cross referrencing the bearings, rather than the whole spindle? Surely there must be some carry over on bearings on 3/4 tons to later models. Using P-30 parts sounds good, but I've personally never seen one that didn't have dual wheels, and most of the later ones had IFS, too.
I do think that this is the right track to follow, though, just possibly not the right parts path.
That rotor that you have pictured is designed to go behind the hub, note the large squarish hole in the center. That's to allow it to fit over the bolt flange for a sealed hub assembly. It's held on with the studs from the backside.
