I know the differences. I own both style boxes.

Well since we were talking about the box I was talking about the rear track width. Just comparing the stock specs the F250 is 2" wider. If you are running the stock rims with the stock tire size no problem. But if you are like most people that run wider tires on different rims you could end up with tires sticking out past the fenders with the narrower box.

That's why I mentioned the width differences.

 

My comments on the bed were meant for the OP, not everyone is aware of the differences in the bed and tailgate widths between the F100 and the F250. My question on the track was meant to clarify "track" vs flange-to-flange width of the rearend. I was not aware of a difference between the rearend widths...track dimensions can be confusing when you are running anything other than stock rims. I have found that it is always preferrable to use flange-to-flange measurement which takes the wheels/tires out of the equation. I have actually used the F250 tubs on my short box to give me more clearance...

 

Hey man if you have the flange to flange measurements for both feel free to post them up. I didn't bother measuring my 56 F250 rear diff before I cut it up and scrapped it.

 

I do not...I always assumed that they were the same as the F100. Since most folks build SWB trucks and, when they do, they swap out the stock rearend for a 9", I never paid too much attention to the stock widths. The only way that I had access to the wheel well tubs from the F250 was from a buddy who had a set of old bedsides available that no one else wanted.
There is another interesting point of trivia with respect to the F250 bed...the wheel well tubs are not centered over the axle. From what I can gather, the factory had a miscalculation when they stamped the bedsides for the tubs.

 

Thanks for the correction...Gonna have to get used to the Inline engines vs the V type...