how to determine if drivetrain is original

[circa55]

Newbie and new owner of a 77 Power Wagon Adventurer.
I'm finding resources do not compare to those available to Ford and Chevy owners.
How can I verify if my drivetrain is original or even equivalent to original equipment? I cannot find a build sheet anywhere in the truck.
I appreciate any help you can provide.
Thanks.

[74w300uteline]

vin # minus last 4 digits

Should give us something to work with. post vin# with xxxx in place of last digits.

[DODGEBOYS]

half ton = dana 44 front full-time / 318-360-400-440 engine / 727 tranny / 203 t-case / chrysler 9 1/4 rear

if its got a big block ford motor and chevy rears it might not be original

[circa55]

vin

Thanks, guys.
The VIN is W14BJ7Sxxxxxx
I was hoping to be able to determine from the casting numbers if my drivetrain was original. I know that the 400ci motor was the correct size based on the "J" in the VIN, but that's as far as I can go.
I would ultimately like to know if the drivetrain is not only true to the VIN, but if it is original. Since I have no build sheet I don't know how to verify anything.

[DODGEBOYS]

that my son you,ll never know even with the build sheet / trucks are NOT marked like a 70 HEMI CUDA / so a numbers matching frame off resto will never happen on a dodge truck / other than a 78 or 79 LIL RED EXPRESS / and thats only because the people in the know way back when DOCUMENTED them when they were still fairly new / and the build sheet stuck to the gas tank was readable

if your truck has the stuff l listed above thats as close as your gonna get



You entered the VIN Number: W14BJ7S345876

W1 MODEL DESIGNATION W100 or W150 for 80
4 BODY TYPE Conventional Cab W/Sweptline (Standard Box)
B GVW CLASS 6001 to 10000 lbs
J ENGINE TYPE 400-1
7 MODEL YEAR 1977
S ASSEMBLY PLANT Warren Plant No 1
345876 Sequential Serial Number

[circa55]

Thanks, Dodgeboys!
Do you have any resources for decoding the numbers that I find on the components, so that I can identify them?