Check your casting number on the back ridge/bellhousing mount area behind the block. Check inside the back of your harmonic balancer, it should have this extra chunk of metal around the inside partial circumference for a 454 balancer.
Then have a look above your oil filter mounting area for the difference between 2-bolt engine and a 4-bolt (hi-performance LS6 or LS7) application.
If you are lucky enough to have an LS7 , there MAY be a clue here in this location. But 1972 strikes me as a little early for the use of the LS7 'XCH' suffix code in this location, I doubt you will find it here but there is an outside chance I suppose .
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