It is the oil pan that is causing the clearance issues. 6.5 vs 6.2 pan molding / modeling differences are the cause of the clearance.
Here's a 6.5 pan to which I've added the markings as follows:
The blue shows where my 6.2 pan differs as the 45 ish angle highlighted in yellow is not present on the 6.2.
Additionally, the orange area pounded / molded into the 6.5 pan isn't present on mine either.
The Red area is where my differential's offending cooling fine would line up.
Here's a couple of shots of my 6.2 pan with the differential out of the way.
Side view of the 6.2 pan

While there is a small notch formed to the left of the oil drain plug (which is further forward than what's molded into the 6.5 pan), that's not where the offending cooling fin almost comes in contact with it.
My granddaughters came over and we removed the front driveshaft and dropped the differential.
Once out, we separated the passenger side axle tube, removed the axle and leaking seal then put it back together again. I've not done this task before so it was an adventure for the all of us.

It's all back together now and on the transmission jack. Tomorrow I'll grind off the cooling fin to gain the clearance and make offerings to the front differential spirits that I put that one washer back correctly....