No, you don't 'pack' rear axle bearings, they should be pressed on and they're sealed bearings (already greased for lifetime of bearing, mine lasted 40yrs...).
The seals should insert from the outside of the axle flange, make sure they're fully seated and lube them with some grease or diff. oil so they're not dry. Be careful inserting the axle so you don't tear the seal.
Once the axles all the way in, turn it a little to make sure the splines are lined up, should slide in a little and the drive shaft will turn when lined up. Then put a short piece of 4x4, etc. wood on the end and whack it with a rubber mallet, should click in another ~1/2" and you're done.
Jon
__________________ '67 Coupe 289 C4, Candyapple red w/red deluxe int., PS, ext. decor group, light group, foxbody seats.
Next to install> stroked 333, AOD, 9" w/3.50:1, PDB.
'09 Black Warriors In Pink with glass roof - the wifes Mustang.
"If it ain't broke, I haven't fixed it yet" -Jon | 
Do I need to pack the bearings on my axles? 
