The typical dealer-installed roof racks were of a similar design to the ones found on Ford station wagons of the era, but obviously shorter.
I have one on my '77, and the previous owner was a Bronco collector who loved them, and had one on each of his four Broncos at one time back in the 1990s.
There was also an even shorter version that Ford dealers sold for the trunk lid of the full-size convertibles back in the mid to late '60s. Saw one on on a 1967 Galaxie XL 7-Liter at a show once.