[jimjaz]

The story I heard from my brother-in-law who worked at GM for over 40 years told me the following about the plaid valve covers;
1) They were never offered already on the trucks from the factory.
2) They were made at the factory and sent to GMC dealers.
3) Folks who bought a 1963 model would bring their truck in for "valve train noise" under warranty. The dealer would adjust the solid lifter tappet valve train to spec's, and to identify the truck as having been serviced and the valve train adjusted, the owner coached on the differences in solid vs hydraulic valve train, and the added plastic "plaid" over metal quiets down the tappet noise as plastic is a pretty fair noise insulator in this situation.
4) He did not know why this did not continue into the 64 model and beyond, but this is why they are only correct for a 63 model truck.

For what it's worth.....