1971 never had any welding
You'll find if its been working in a gas terminal it will be diesel. I once done a job in an oil refinery complex and my boss wasn't allowed in cos her car was petrol. Something about the spark ignition on the petrol.
yes, spark ignition is not allowed. Even diesel motors should have a spark arrestor and chowlin valve fitted to the exhaust.
Do you have the Vin number? chucking into Calvin might throw up some info. Let me know and i will do a search for you.
G