The attachment piece for these shackles is what is different on the frame. 3600 shackles, 4000, 6000 Series are all the same with the holes in vertical alignment. The 3100 shackle has an offset bolt pattern, here is a picture of the 3600 type. I do not have a picture of the offset or cabover (unique style)but they are shown in the 1947-54 Factory Assembly manual.

http://community.webshots.com/photo/2275285170102454676BEQvTZ

Last edited by Brad Allen; 02/01/2010 10:46 PM.