This happens to be the same as a GM corporate 14 bolt as well circa 1978. I'm not sure of any dimensional difference because it's been 40 years since I had one apart.I break the rules on a regular basis as you know. My pinion is pointed up due to running a rear DC shaft, so, when I fill the rear diff I point the nose of my rig down the incline of my driveway so as to overfill is a bit. Haven’t had a problem yet.
So basically, our rear axle was not designed to use oil bath as the lube for the wheel bearings. This discussion has been had before. Refreshing the hub oil by going off camber side to side is a good reason to go wheeling. Most wives, will understand and agree. LOL
It's actually listed in their manual to pre-grease the bearings then allow the grease to be "absorbed / blended / dissolved" into the gear oil that enters the hubs. That's why it's very important to use compatible greases and oils in your truck.