t-20 model number help

[Heaven's Pavement]

I have a T-20 out of a early 70's MaxII.
Trying to find which one of these numbers stamped into the housing are what.
On the gear side between the metal "fins" 13-13-065.
next "fin" over..406
and somewhere else was stamped 58 E643.
Anyone know what these mean???
Thanks in advance for the help...HP