Ok, of the three that I have been able to find, (ChevyCrew, Dirty Anton, and now Cable810's), everyone is using the Ford 36" spring width axle.
In ChevyCrew's thread, he mentioned this was for oil pan clearance, as a 44's pumpkin is offset more to the center of the axle, and would likely interfere with his oil pan.
So... I'm going to ASSume, that this is why Dirty Anton and Cable810 followed suit, which is fine, I have a 89 kingpin 60. But I also have a 78 HP44 HD, and... My Trailblazer is a 5.3. There's like, a million 5.3 oil pans out there, with sumps all over the place.
So, long story short, is the oil pan the only reason you guy's are choosing the wider 60?