i want to change my 91 regular cab to a extended cab and was wondering if i would have to do any modifications. i will be making a flat bed soon thats not a problem.

 

Well you will have to strip your truck the bare frame.Then take the all the body mounts off.Then put an ext. cab on the frame to mock up the location the body mounts.Then make new body mounts and weld them to the frame.Then put the ext. cab on it.Then reassemble your truck.Possibly you will have to extend the frame to fit a decent bed on there.I say just buy an ext. cab truck.

 

Yes. You will need to do modifications. Reg cab/short box trucks have a shorter frame. Since you are making a flat deck thats not really a problem, but you will need to figure out some custom mounts to make the cab work.