1974 GMC Truck type of oil

this truck was bought from an old man that dis wonderful maintance on this truck. he always used 10w30 valvoline.
i bought this for my 20 year old son. im sure their driving styles are different.


what type oil should i use? the same as the old man or something else.

it does not leak or use oil. it was changed prior to me buying it.

thanks