I agree with Bill regarding the rarity of 3-window vs 5-window.
"In the day", the 3-window was much more common. They were cheaper. I never saw a 5-window in the 60s and 70s (on the roads or in the junk yards). It was only when I got into restoring my 54 Suburban (in 1994) that I learned about the 5 window cabs.
It may now seem that 5-window cabs are more common - that might be because they are more desirable and/or they have survived because owners took better care of them?
Of course, my experiences were in VA/NC/MD and the majority there were farm/work trucks.
