Can it be done? Sure, no doubt. But there's more parts to consider than just splicing in a new piece of steel and fish plating it. Call around and get some quotes, if anyone would even do it, I have to think it would be either cheaper or the same price to just trade your truck and buy what you want. You could get the manual and v10 up until 2010.

No body shops around here would even fathom doing something like that, a truck fab shop might and they're the experts on stretching frames b/c they do it on big trucks all day. There's a lot of differences between a mack and a superduty though. Most important thing - they don't work cheap and this isn't a small project.