This is a pic of the Standard “pancake” air cleaner found on 54-55.1 3100 trucks. It may have come with other 54-55 models.

Second pic is from 54 Truck Operators Manual.

Does the engine being discussed here have hydraulic lifters? Seems like you all have it ID’d as a passenger car engine and the type of lifters would help nail it down.
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1955 1st Series 3100
ol'55