As posted above, a 5-window can was available as an option in all Advance-Design and GMC New Design years. In some years, the 5-window cab was available without being part of a "deluxe cab" option.
I you are picky about cab details, I think the 47 and 48 cabs had a slightly different firewall compared to later years. Also, you probably know that the early cabs did not have an opening for an in-cab fuel tank.
