Hi, Awesome truck. Looks a lot like mine!! Although, i've restored mine to this condition with as much original parts as possible, minus the tailgate as i wanted to find a pretty rust free, straight and usable one. Plus, it's an easy fix if i do find a good original one.
The short bed bedsides are 80" long. Your truck is definitely a long bed with the data plate on the kick panel, it tells you that information as well as the paint code/trim codes.
If you had a 4x4 shortbed fleetside, that's the money, although what you have is awesome indeed and what a great find with the parts too!! If you have any interest in selling the short bed parts, let me know as i have a place/home for them!