Well, I had put out several feelers when I posted here and had a good hit this morning from a friend via email. So, if anyone is interested this is the way the GM tag on the trans will be decoded. As well, my Z28 is a Jun build and thus the April Julian date is perfect a perfect timeframe to have slid that into the Z28 just two months after it's birthdate:
these #s you gave me were from actual tag riveted to side of trans right? "YES"
if so, these are TurboHydramatic/GM company #s
the 506 is upper right hand, and stamped. probably before this # was printed on tag
and no longer legible; so it goes:
70W 506
then stamped below is CW 70 3935
which is :
70 model yr
W engine code trans was to be mated with (ex. 69X = 1969RS Camaro, x=ZL1 eng.)
506 is julian date when trans made=
(1/1/70=366, so 506-366= 140; 04/20/1970; 20th April, 1970)
the 3935 is sequential production number from plant on assembly line.
(so they know which car they put this in- three thousandth, nine hundreth, thirty-fifth)