I have a 69 w th350, 2.56 rear...was told to check my no. and where ,but I couldnt find it!
later took it by a friends house, he located it ,excactly where they told me to look....its very hard to see....maybe use sandpaper or something to clean it up...leaving dirt in very faint indentations...mine was about 4"-6 " out from drivers side brake drum, facing straight back....
its a 2 letter code...