What happens in California is......After a vehicle doesnt show any activity ie; registration fees being paid,or a non-op being filed,(especially after 30 yrs.) the vehicle gets purged from the system. As far as D.M.V. knows, your truck doesnt exist.
Keep the old title for sentimental reasons.
Go to DMV and tell em you just got the truck,lost the paperwork,and want to register it. When they run the plate number it'll come back "not on file".
Pay the fees,get it verified and youll be good to go.
Good Luck,
Marty