Most campers are made with a specific model of cab in mind, ie. regular cab, super cab or crew cab.
Mine is made for a crew cab only. If I put it on a regular cab, the overhead would extend to the front of the hood.
Besides making vision a problem, the center of gravity would be all screwed up, making handling a big problem.
On most of the newer and larger campers, the overhead is the same length.
East-West or North South beds make no difference in overhead length.
On an EW bed such as mine, the front of the overhead is where the closet is.
On the NS model, the closet(s), are on the sides of the overhead.
2011 F-350 DRW,4x4
2011 Host Everest, triple slide
20' Rogue Marine jet boat.