Frame shortening question

[Karcastic]

Hello,

I have a 98 RWD B4000 and I would like to shorten my wheelbase to a reg cab short box length so I can use as a chassis and drivetrain donor for an older f100. I've searched everywhere and can't find out the frame differences but noticed something about the frame being two piece and riveted making shortening to reg cab shot box easier I guess... Am I right in thinking that the frames of a short box reg cab and a ext cab are the same just longer/shorter in the middle? Could I just cut out the required "unknown difference" straight frame section and use the driveshaft from a short box reg cab?

Any help or advice is appreciated

By the way I'm thinking of a 51 or 48 f100 maybe even a 53-56... Depending on the cheapest one I can find.

 

[Karcastic]

Update..

Saw the two piece location near leaf mount... The frame is not level all the way to the cab so that idea won't work. So now I'm wondering where to make the straight frame section removal cuts under the cab. Does anyone know the frame differences between the reg cab short box and ext cab short box? I'd assume the frame is just lengthened the 14.3 inch difference in wheelbase under the cab..?

 

[alwaysFlOoReD]

I can't help with your specific question, but I can give you a link to a ford pdf on lengthening frames. The principles should apply to shortening. This is one of those modifications where if you don't know what you're doing you could KILL someone. Please be careful and use professional help where necesary.

http://www.therangerstation.com/forums/attachment.php?attachmentid=9158&d=1358836447

 

[don4331]

Karcastic:

The difference between regular cab short box and long box cab sections is a 6" extension to the rails just before the front spring mounts.* But, the super cab, cab section is deeper/narrower/thicker in addition to being 14" longer (8" longer than long box regular cab) than the regular cab. Maximum Side Rail Section: 7.64x2.55x.16 versus 6.54x2.89x.13

Frame is quite curved all the way along; you would be better off getting a regular cab frame to start with.

*The long box bed section is also 6" longer behind the rear wheels.

 

[adsm08]

Also, have you found your other truck and then sat down and taken measurements? The F100s were bigger than the Rangers. You may find that the cab section is already the right length.