The vin number is on the passenger inside A-pillar between the two door hinges Unless it has been removed
i had a 47 yrs ago. (about 37) on the firewall is a badge plate with vin #'s. in fact, this was my 1st car and my 1st car i totaled out. i still have the vin tag and title also a vin plate on the driver's door pillar
In Texas (possibly other states,) ~pre '55 GMs always went by the motor numbers rather than the body numbers. If that's so, usually we'd "find" a motor that matched your title.