Lubricant suggestion for Dana 60 Full Float

My '82 F-250 HD (4x4) has a full float Dana 60 which has been a fun to learn about.  I have a seized emergency brake cable to fix and I'm going to have a look over the condition of the rear brakes at the same time.

I'm trying to figure out the best lubricant option for the bearings.  The Ford shop manual only mentions an oil bath using "Multi-Purpose Lubricant Ford Specificiation C1AZ-19590-B" or equivalent.  The Dana manual mentions either packing them with bearing grease or an oil bath.  It states 80W-90 mineral based oil or 75W-90 synthetic.  It also mentions not to mix mineral and synthetic oils.

I have no history on this part of the truck.  If it has been touched, it has probably been a a long time.  I have no idea what lubricant it has now.  How important is it not to mix the lubricants?  I'd rather not have to drain the differential at this point.

I'm assuming once everything is back together, I should also check and refill the differential?  I haven't found that specifically stated anywhere, but it seems necessary if the axels are being pulled out and oil is going to leak out in some manner.

You pack them with grease so the bearings and seals don't start dry.
Under operating conditions gear oil is sloshed side to side while cornering or driving on slopes and it gets to the hubs.

Back in the day it wasn't recommended to mix oils but things are pretty compatible now.
You can be sure it didn't leave the factory in 1982 with synthetic fill.
If it's an old diff there's no point in paying extra for synthetic, though I would be wanting to pull that cover and clean it out.

Also, make sure the vent is clear and hose properly attached up out of the way.
You don't want water getting in or pressure building up.

What's your climate?
How hard do you work your truck?
What kind of oil change intervals do you follow?
Is your D60 LS or not?  

You definitely need friction modifier for the clutches if it is. (either formulated with it or a bottle/tube of additive)

I'm in southern Louisiana so the climate is hot and humid most of the year.  The truck has 139k miles on it.  It was a farm truck but it was well cared for until about 15 years ago.  Once the original owner retired it didn't get much use.

My eventual goal is to drive it almost daily, hall lumber and pull a teardrop camper (occasionally).  I'm planning a trip to Arkansas in April and I do intend to drain the diff before then.

I do have to check the vent tube further.  I noticed it looked broken and potentially clogged up with mud.

According to the numbers it is limited slip.

I'd go with conventional 80/90 w/ LS included

You're not overloading it and will mind the service intervals

Thank you!  That is what I did and after finishing the brakes and putting it all back together again it's running just fine.  Sometime in the next few months I'll tackle the differentials covers and refill everything with fresh fluids.