8 3/4 rear end confusion

So should I put it in neutral and spin the rear end to try to line up the secondary splines?

I’d put it in neutral and have someone rock the driveshaft back and forth a bit when you’re sliding the axle in. Might take some fiddling to get them lined up again.

Also, before you get carried away, have you checked to see if the thrust button is still in place?