Dude, its called a custom driveshaft! length is not an issue. The only limiting factor is where the shifter would poke through and even that can be fixed with a relocation kit of some kind. When customizing keep in mind that there is Always a way!
Btw, I found that the six speed in the concept was a Borg Warner from a C5 corvette. If GM can do it so can I! Now I just need some parts ...and a car!