Dana 60 in 1970 GMC C2500

[SonomaComa]

I have a Dana 60 Rear End in my 1970 GMC C2500 with rear leaf springs.
In the hub I just replaced Inner and Outer Bearings and Seals while replacing the rear brakes. I drove about 15-20 miles and noticed something was wrong. Took the right rear Drum off and the bearing blew apart! Immediately checked the oil and it was fine less than 1/4" below the fill plug. After looking real close I noticed the bottom of the fill plug is just about dead even with the bottom of the axles! Should I park it facing downwards on a hill to fill it? Or on a slant with the left side lower? I was very shocked that the GL-5 80w-90 Gear Oil was not all over the place.