According to the 1950 Vehicle Information Kit
3100 front track of a 3100 is 56-9/16" and rear track is 61"
6400 front track is 58-3/4" and rear inner track is 57-3/4" and rear outer is 79-1/4" with average rear track of 68-1/2"
So while the front track is slightly narrower, the rear track is wider on the big bolts.
