VIN Code Question

Hi Folks,

Just got my 1972 Duster (Happy as heck about it!), I ran the VIN through the site's decoder and got the following:

Vehicle Model: Valiant/Duster/ScampVehicle
Class: Special Price Class (Duster 340,Barracuda Cuda)
Vehicle Body Style: 2 Door Sports Hardtop
Vehicle Engine: 340 CID/240 HP 4 BBL V8
Vehicle Year: 1972
Vehicle Assembly Plant: Dodge Main, Hamtramck, MI, USA

The tag on the door shows "9-71" above the VIN Code (which matches the plate on the dash.) Would this indicate the build date? Guessing they were producing the cars for "72" in late 71.

Also, what is the best/easiest way to determine if the engine/trans are original? I have found references to casting numbers, but I am not clear on where these number are located. (Forgive my ingorance, you gotta keep in mind that I have been a Chevy guy for the last 30+ years...been a MOPAR convert for 3 days! :newb:)

Thanks in advance.