On the task force body style, 1955-1959, the GMC hoods began quite different than Chevrolet. Beginning in 1955 a large opening, 5.25″ x 25″, was used to hold a set of die cast GMC letters attached to a decorative grill.
In 1957 this grill was removed in place of a perimeter ring. Why the less attractive ring was added is a question. Possibly this grill held leaves and restricted some air intake or maybe it was a change just to be change. There was no hood opening in these last two years of this series.
By 1958-1959 GMC and Chevrolet shared the same design hood with only trim differences.
1957 Standard (above)
1957 Deluxe (above)