Need help identifying this rear axle...

[Gypsyman]

I've been browsing for a disc brake front and rear set-ups to swap into a '63 C60 that I brought home and I ran across an odd combination that I don't seem to be able to identify.

The seller claims that both the front and the rear came from a mid 1980's GMC P35. Possibly an old Matco truck. Lug pattern is the standard 5 front - 10 rear that you would expect. The front looks like a regular step van A-arm setup but the rear is not what I'm use to seeing in this application. It a HD, front drop out, square tube axle like my small Internationals have. I'm hoping that the tubes are stamped with some kind of identification but I haven't been able to see the items in person yet.

The center chunk has the following markings...

JES3891
5 43

That's about all that's legible. I'm assuming this indicates a 5.43 gear ratio but I can't find anything regarding the JSE3891 marking.

Richard