[dhaymaker]

There are a number of very experienced builders here with threads on this subject. I would look up one of Kevin's (Lewis Fabrication Designs/Rokcrln is his username) threads to see a good example of the process. Seeing one of the beds cut down would probably give you some tips and ideas as to what to look for. Need to pay particular attention to how/where the bed was shortened. You want to ensure the mounting points are going to match up. This isn't an insurmountable issue, but you probably want the cut down bed to look as "stock" as possible. If you have access to a friend with a SWB truck, you could get some comparison measurements, as well.

There are other examples here, so I would look for a couple of them to get some ideas. I'm sure there will be other responses, soon. Good Luck!