Small back window 70 cab ???

[gmc71]

Does this really exist? I was under the impression that only 67 had the small back window. The truck in question also has a PTO on the transfer case so I was thinking it may have originally been a tow truck ( the bed is long gone). If this is some rare option, is it worth anything to anyone? The cab is in great shape, only a bit of rust in the drivers side cab corner, and a tiny spot on the fire wall. Am not sure if if it was power brakes or not. Floors are solid, small patch panels already done.

If anyone has information let me know, if its worth I may sell it.

-Ben