If you are building a speedster with parts from numerous years, would the frame year make much of a difference?
The 1926-7 chassis has a wider & stronger rear cross member to start with...Dave C.
Frame is slightly heavier(thicker) and if you use it,be sure to use 26-27 parts that bolt to it. Nothing else will line up properly. Drilling new holes is a bear. The front fender irons are fun to get to work also.(if you;re putting fenders on.)
The front fender supports is pressed steel on 26/27 frames instead of a thin forging on the older frames. Here is a picture with a late 26/27 frame to the left and a 13-25 frame to the right (from one of Hap's postings)
The front crossmember is different too, along with the new style quadrant, and serial numbers on the frame. There are also two styles of rear crossmembers.