Hello! 81 Dodge D150 with a 273 V8

Good evening, just bought a 81 Stepside with what the previous owner said was a Commando 273, joined because I gotta figure this truck out and have some fun! What do I look for to see if this in fact a 273 or a 318?

Side of the block just a bit under where the block and heads meet on a 318.
Not sure on a 273.
Welcome to FABO, and they do have a trucks specific site here also.
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