For those lookin to put an older cab on a modern frame...
I had considered a 39-47 cab fro my 1980 (still am if one appears), and ran across a 47 at a show.
I measured the frame and cab back to front axle center line.
The frame on the 47 was actually 3 inches wider than my 80!
The cab to axle distance was identical (6'3").