360 HP Confusion. History of this motor?

It appears that there was a 360 4bbl "J" code E56 motor from '73 to '80, at the same time that the E58 motor was available. Guessing that means a block stamped with "HP" was more than just a different intake.

It does kind of seem like I used the pan in the Diplomat build I was doing at the time. Really foggy about the specifics though, can't even remember what motor I put in that car. I know I put a 360 in the Diplomat, I know the pan was missing off this motor, and it doesn't make sense I bought it without a pan. This would lead me to believe that it had a car pan on it, not a truck/van pan.

If the VIN stamp on this motor had been 0A135520 instead, I wouldn't be here asking the question. Just makes no sense to me.

I guess I am going to go with it came out of a 1980 cop car and the "A" in the VIN stamp is a mistake.