1946 was the year the federal government allowed GM to sell to civilians after WW2. My grandpa dashed down to the dealership to be the first to buy a new truck.
If the truck was mine, I would risk removing a few screws on the side lifter galley cover and peek inside with a flash light. No more guessing. Figure out what lifters you have before making adjustments. If they are solids and light tapping, that's music to the ears. Means they are not too tight.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
