Solid axle I assume.
Can you get spline engagement at all?
Birf stuck out too far?

If it's a "little" long, you can cut off a small amount from the splines from the axle shaft on the diff side.

If it's not slipping in at all, keep workin' it I guess.
Pushing down on the axle at the seal, to make the axle tip up on the inside. Reach over to your driveshaft and rock it back and forth a little.

85 4Runner - With NEW Marlin 4.7 Gears!! It's a whole new beast!