I am no Model T expert but I have always wondered if all T frames are the same. If say a 23 frame will fit a 27 or not?
26/27 frames are different from the earlier frames. 09/25 frames are essentially the same, dimension wise, though there are many minor differences in hole spacings, brackets etc
The main difference between the early frames and the 26-27 frame is the wide rear crossmember used in 26-27. Length and width are same in all years. Wheelbase 100".
front end is "pinched" it is smaller then the back my wheelbase is 108 ('27 roadster) http://i12.photobucket.com/albums/a236/TrackT/100_2122.jpg
Stock Ford 26-27 chassis has front crossmember "ears' to attach the fender brackets, and the rear crossmember is wider. 1915-25 are about the same, but running board brackets differ early/late. 1909-14 are worth a good buck to restorers.