1969 426 Hemi valve cover markings

[hemi68charger]

hey fellas.

Looking to figure out the valve cover markings on the valve covers for a '69 426 Hemi w/727. I see on Jimbo's GTX, #21 is used on the passenger side ( last 2 digits of the complete motor assembly part number if I'm not mistaken  ).

The passenger side has a set of numbers too? Maybe designation of tranny type?

Thanks Jimbo !!

[hemi68charger]

I see this on a Mopar Muscle online article, make sense? I see Jim's GTX has only two digits where as this Road Runner has three.