Ok, I just measured my cab. I don't have a suburban, but you are saying the front of the cab is the same, which makes sense.
Ok, the first picture is showing how I made the first measurement laying right on the top of the rear of the seat frame, I don't know if the suburban has one like this but here you go with this measurement. We are talking windlace holder to windlace holder, 60 and 3/16 inches.
The next photo shows me using a tram to measure exactly down where the door jamb meets the floor. I put the tip right exactly as you see on the other side as well, so this is a perfect measurement of my cab. The third photo shows where I am a little better so you have a good idea. The forth is the measuring tape laying right on that tram with the distance of 57 and 3/4 inches.
And here is an "Basics of Basics" to using or making a tram and how to measure stuff like this.
http://www.hotrodders.com/forum/basi...ng-319474.html
If the Photoscumbucket photos don't open for you, let me know, I have them saved and I can post them. I really need to post this here with the photos so they will be saved instead of on photoscumbucket.
Brian