To continue with the discussions on the hoods on the 1965 Plymouths, I got the scoop on the scoops and hood emblems from a guru and owner of one of these cars, Harold Laplatte.
These cars came with the scoop and the hood emblem installed from the factory. I think it safe to assume they had the "426" insert in the emblem given they went to the trouble of putting a hood emblem on the car. I'd think the factory would want people to know it was a 426 equipped vehicle. A small tidbit of information he offered - the holes in the hood were punched, not drilled.
As a side note, I have a complete collection of these hood emblems that I've gathered over the decades in my collection for reference. Taken off of cars or picked up at swap meets, not NOS.
Akron Don