ChevyGirl - the 55-7 cabs are identical, the 58-9 are a bit different than the earlier ones in the firewall because of different hood hinge arrangement, and it's a bit painful to use the earlier front clip and hood on the later cab, tho perseverance can make it work.
there's also a little difference in the central part of the firewall stamping to accomodate the later style gas pedal and the V8 throttle linkage.
the window replace is possible - I saw one done by a guy who's an exceptional bodyman, and the best way to do it is to cut across the back at the belt line, and cut the windshield pillars and take the whole top - don't think I'd trust just anyone to do it if were mine . . . good luck!
Bill
