Beginner Question: How to tell 273LA from 318?

Admittedly, I am relatively new to mopar restoration. I purchased a 65' barracuda about two months ago under the pretenses that this was the original 273 but am starting to think I have been bamboozled!

That being said, I am not sure how to tell if it has been swapped without pulling it out. Anyone able to help? I can get your any additional information you might need but lets start with couple images.


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Here's a thread on how to ID a small block...

How to ID a Small Block Engine Block: