Deciphering My Rear End

[bddcustoms]

Hey,

I've got a '69 C20 with a full float rear end (on coils), and 4.57 gears. It's either an HO52 or HO72. I've read (mainly from posts) that HO52 was for 3/4 tons, while 1 tons got HO 72s. But Randy's Ring and Pinion says 3/4 tons got HO72s also. Here's what I've been able to visually verify about the axle under my truck:
- 10 bolts
- 3rd member
- pinion bearing bolt
- "HU" stamp (4.57 gears)

Other visual ques are undecipherable by me, and I'm hoping for some help and feedback from ChevyNation. Specifically, next to the pinion bearing bolt appears a 7-digit number, a six-spoke wheel icon, the letter "D", and the number "2" (see image). What the hell?

Ultimately, I want to swap in disc brakes, which I believe I can using 14-bolt kits. I would also love to get highway gears. This is a cruiser. I've read a few places that the aftermarket offers 3.90s but I can't find them on the web. Any hints? What about lockers or limited slips?

I purposely chose a 3/4 ton LB because everyone on the custom scene is doing C10 SB. I want the this big boy to be sexy and trick but still true to itself.

Any direction or perspective you might offer is welcome and appreciated.

David