Determining a match of a 73 Satellite Big Block car and it's 400 Engine

[Bluesky10]

Hello all and thanks for your help and advice in advance.

I bought a 73 Satellite originally as a doner for its floor pan, rear quarters, and various bolt on parts on my son's 74 Road Runner he is building.

After picking it up we discovered it had a big block K-member, and the VIN identified it as having a 400 in it. Along with the car the guy tossed in a "440". After arriving home and looking thru everything, we realized it was a 400 and not a 440. Following up on this to determine if this was/is the original block.

So, how can I make the determination of weather this is the original or just an extra engine to store?

Thank you

 

[70chall440]

Look at the partial VIN stamp on the block right above the oil pan lip.

 

[RemCharger]

Yup shouldn't be hard. J400 on the pad with a date not long before the build date