[Mr70]

I think his dates are wrong.12/68 sounds better.
I haven't seen any 1968 Chevelles with white letter tires from the factory.They started putting white letter tires on Chevelles in 1969,so those early built cars might not have gotten them.
The 12/69 production date is heavily into the 1970 cars Production time and the Aug-Dec.cars have been documented with white letter tires by then.
The Brands available from the factory were: Goodyear,Goodrich,Firestone,General,and Uniroyal.Buildsheets did not specify tire brands.