WHOA there, post photos, I don't think they were different. A '48 here used a split windshield and I believe it was the only one an AD had no matter where it was made.
This image is deceving in that it says "'54-59" and those were two VERY different windshields 54-59, VERY different.
Here's a 54-first series '55.
And here is a second series '55-59
If you're windshield doesn't look like this PLEASE post a photo of yours.
I am very interested! I am a big fan of these trucks and their designs that were tried and not used and of GM Motorama and all that so I would love to see your truck if it used something different there, that would be very cool to see.
GM Motorama http://en.wikipedia.org/wiki/General_Motors_Motorama
Brian