1980 C10 Mystery

[3kgtjunkie]

I purchased a 1980 C10 a month or so ago, and have been trying to label what has been done to it by the previous owners. According to the VIN, it should be a 1/2 ton 2wd inline 6. However, it has an 8 cylinder motor and is 4wd... I'd like to know what parts have been swapped out, so I can properly maintain this truck, but I haven't been able to identify anything specific yet. For instance it appears a gasket on the transmission is leaking and needs to be replaced, but I can't figure out what kind it is to find the part. An additional mystery, which may be simple, is the vin position to identify the year is an 'A' instead of a '0' which I was guessing would still make it a 1980. Below are some pics... help?
Body:

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Motor:

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Some markings I found on the trans last night.

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[RetroC10Sport]

Someone likely swapped that cab on to a 4x4 frame.

Yes, A is 1980.

 

[CSFJ]

I'd be more upset at whoever bolted the Ford mirrors on the doors.

 

[3kgtjunkie]

Any idea where the vin might be on the frame?

 

[yevgenievich]

Take a picture of the trans pan. Most can identify by shape instead of numbers

 

[RetroC10Sport]

Any idea where the vin might be on the frame?

Passenger side rail, on top below the cab. With the cab on, it can't be seen without a mirror.

Take a picture of the trans pan. Most can identify by shape instead of numbers

Looks like a manual, no pan.

 

[yevgenievich]

I should have stated over all bottom of the trans