To start off I really know nothing about differentials and I’m trying to learn about them as well as my truck. If I ask stupid questions or don’t understand an answer I apologize I’m just trying to figure this all out. So I know I have a Dana 70HD in my 73 dually. It’s cast into it so I’m pretty sure I have that much right. Above that C34764 is cast into the housing as well. I don’t know if that means anything or not. More the part I’m trying to figure out and decode is the stampings on the ring gear. It says 7 21 72 DANA 34837 B3R28X 41-11 And then about an inch further it says 272 After counting the teeth on the ring and pinion I get 41 ring and 11 pinion so I believe that to be 3.72-1. What do all of the other number mean? If anything useful I guess. The tags are no longer on the cover bolts. I assume at some point someone has been inside of it because those are missing and the bolts are all stainless which I don’t think is factory. But I also don’t know that for sure. Maybe they are? I don’t know anything really about LSD’s but what I have gathered is if you spin the pinion and both tires spin the same direction then you would be looking at some sort of locked diff. Either locker, Lincoln locked or an LSD etc. If I spin one tire only that tire spin but if I spin the pinion both tires spin the same direction. So I think LSD?? I really don’t know I’m just spit balling. Between my little knowledge and speaking with MR. Google I’ve come up with more questions then answers. So if anyone could toss an answer or two my way that would be pretty cool.