I've cut up and or owned probably 30 78-79 ford trucks from broncos to F-350s.
Every automatic truck had 3.54 gears
Every manual truck had 4.10 gears.
I'm not sure if it was always that way, but I'm starting to think so. I've never seen anything different, although all the trucks I've had have been 351/400M or 429/460. I've never had a small block or six popper truck.