Am I justified in my frustration?

All 8.75s have a center spacer captured by the cross-pin. The longazz punch idea will not work.
My guess is that the clutch is seized on the axle splines.
Or, if a cone-type, then possibly the two splined parts are slightly out of sync, and or also seized on the axle splines.
I think you will have to rock the axle back and forth, with the pinion locked, to break the rust-bond.
Just guessing.