Dana 44 rebuild, finally ready to order parts, need a little help

Ok,
The JC Whitney hub puller came today and worked great so I'm ready to order some dana44 parts. 1970 cj5 v6
First of all I have researched and read when rebuilding one of these units you should only use a inner seal if there was one there. Well on mine there were no inner seals, but how would I know if a previous owner didn't replace them at one time. Is it my choice to use or not to use. I going to use the jeep for running around town and doing a little snow plowing.
Use a seal or not???
Second question is a spreader required to put the differential back in with new bearings ? Mine dropped out pretty easy and I am planning on replacing the bearings. Is aspreder tool a rental item.
One more question: why do the rebuild manuals say only to shim the axels on the left side? Why the left side.


Thanks!

Thanks!

 

Do the flanges separate from the axles shafts? Are the grease zurks at each end of the axle tubes?