Where/How do I verify tht a 442 is a 442?
The VIN # is 3G37T5M180751........What size engine is this?

 

That number won't verify if it is a 442, Oldsmobile built 6,015 442 cars on the Cutlass body that year as an optional package. You won't know by the vin but here is the breakdown on the vin.
3=Olds,G=Cutlass Salon,37=2DR CPE,T=455 V8,5=1975,M=Lansing Mi., last digits are production numbers 8,751st car built of about 42,000 ( they start with number 10001).
You might check with O.C.A. and join their local chapter or a local 442 club. They may have more specific data on which vin numbers were ordered with the 442 package.

 

If you provide the cowl tag info, the engine id number and the trans code I might be able to decipher for you.