trhamilton,
To answer your question: most people who have reported putting a window in a panel truck (or have found windows in a panel truck) have reported just using one pane of glass - not a sliding window.
If someone has information about installing a sliding window in a panel truck, let's hope they post information/advice.
Regarding what you do with your panel truck: I agree will some of the sentiment above; HOWEVER, it is your truck - do what you want with it. BUT, please carefully consider chopping into a truck, if you are not going make use of the truck. Chopping up an old truck that is never completed, leaves a mess for anyone else who might want to no a more "natural" restoration.
