Am I justified in my frustration?

Love how you guys jump on the “That’s dangerous” argument and try to insult me not building rearends when you see this piece of **** rear wont come apart even by pulling it with a 4x4.

All I need to go is get a rearend apart. I send 3rd member to SD Gear and Axle. So what if I don’t build third members. Moot point. I’m not allowed to send a 3rd member to a shop? That's what you're latching onto now to tell me I'm not justified in being frustrated?

You still have to be able to disassemble one to be able to call it rebuildable. The seller says he has no reason to believe the diff is not rebuildable but what's the reason to believe it IS rebuildable. This was a mystery rearend to him but since it's not "rusted like a backeast rearend" ...... Well, my bad for trusting a guy based on his affiliation with a reputable club and a FABO member.


Would it still be considered rebuildable?

I'm just trying to help you from this point on.
Getting pissed off and continuing to struggle with how in your mind you got screwed over isn't going to resolve what you have to deal with now that it's over.
And it is.
Quit complaining.

There's nothing wrong with getting someone to build a gear set/third member for you.

If you used my method of cutting a window with a cut off wheel in the back of the housing, you could cut the axle shaft close to the third member and pull it out.
Then take the caps off and throw away the gear/bearing assembly as well as the pinion and bearing.
That leaves you with the bare third member ready for cleaning/blasting and rebuild.
(A core)

Then put the housing in a vertical press and push the remainder of the axle out.
And if it doesn't come out that way even with lots of heat on the housing flange area above where the bearing runs, then cut off the axle flange above the bearing area.

If you cut the flange off, then you might as well have it narrowed to A-Body width and make a few bucks on the bare housing.
Weld the saved window back in and dress the welds at the same time.

There's more than 2 ways to skin a cat.......