How to ID a Small Block Engine Block:

great info I am a lifelong transmission rebuilder
starting a resto on my sons 75 duster, original 360 auto, sunroof, fold down seats buckets.
the trans is original numbers matching unit, the motor is not. its a 360 casting 4006830-360-3
all thats on front pad is R7
thoughts?
going to pull it next week to send off to machine shop just like to know where We are starting
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