Welcome to the forum, Spikbeatz! Hope you enjoy your stay with all of us wackos.
Wow, tough conversion. The least you would probably have to do is extend the frame with plasticard or sheet stock, plus extend the drivetrain axle. The rear section of the cab could be done with cardstock, but will require alot of sanding and filling to get the curves right. Then, the interior... you could use putty to create the rumble seats, floor curves, and interior trim. Clear plastic sheeting would be my guess for the rear windows. Texturing can be done with a sculpting tool or hobby knife, if you're really careful, but I won't kid you, it's going to take alot of work to make it happen. Good luck, if you decide to do it!
demono69