Your tranny casting number (3845122) matches the tranny number from this post from 2014.
Is This A Saginaw? So, I believe you have the SM 318 3 speed with a column shifter.
Your number on your differential housing shows it is a 12 bolt. Here is a nice article from Hemmings on the 12 Bolt that may answer questions you haven't thought of yet.
Hemmings 12 Bolt Info Hope this information helps.
