J DOT "63 cm" measurement

I picked up a set of TRD Sport take offs (just the rims) from a 2017 for $425CAD and as soon as I got home was notified of another listing for brand new 2019 take offs for $400.
Not being totally satisfied with the condition of the 2017s, I went back to the bank machine and acquired this second set.

Now comparing them I noticed that the 2017s all have 63cm cast on the inside of the rim.
On the 2019s (all with the same date code mind you), this measurement varies. Two of them are 62cm, one is 64cm, and another 67cm. I'm wondering what is this measurement exactly?

 

63 cm is 2'. I don't think it's a measurement.
Maybe it's a casting mold number.

 

Casting Mold would make a whole lot of sense.
I'm crossing my fingers that that's the correct answer.

 

J is the tire bead profile, let me check my files on the 63

 

I see you both have answered tire questions in the past, so while I have your attention, I went ahead and mounted some used Duratracs to these 2019 rims.

OE tires: P265/65R17 110S - Dueler H/T D684 II, Max Load: 2337 lbs, Max Pressure: 44 psi
New tires: 265/70R17 115S - Wrangler Duratrac, Max Load: 2679 lbs, Max Pressure: 51 psi

The door placard on my '08 DCLB shows a cold inflation pressure of 29 psi for both front and rear.

From my research on P-rated vs Metric (ETRTO), my new tires should only run 28 psi to match the load rating of 2149 lbs per tire.
This sounds a bit low considering the higher max pressure rating, so just double checking before I let some air out. The shop that performed the mount and balance inflated to between 34-37 and even at those pressures, the front sidewalls do not "appear" stiff enough.
https://tirepressure.com/p265-65r17-tire-pressure
https://tirepressure.com/265-70r17-tire-pressure

Cheers!

Obligatory "dirty" before and after:

 

No; you're on the money.
FWIW, an ERTRO metric does not increase load passed 36 psi. Anything above this is used to mantain the speed rating above 100 mph.