This subject comes up fairly often - “How do you fill the transfer case on these old Jeeps without making a horrible mess?”

Here’s my answer, developed after 19 years of trial and error.  It’s a pump unit, available at most auto parts stores, with a long section of hose clamped to the end.  This allows the bottle to sit on the ground outside the frame rail, where you can pump it with one hand while holding the hose in the tcase hole with the other hand.

I clamp a bolt in the end for storage.