January 2003 issue of Street Rodder had an article dealing with the '35 through '48 rears with the information you're looking for. I've attached a portion of the page with the table of various dimensions. PM me with your email address and I should be able to email you the complete article.
That said, the article doesn't mention that the '42 through '48 has an unusual spring / shackle / rear end set up. Whereas Fords from the Model T through '41 had rear leaf springs that were much shorter than the perch to perch dimension on the rear. As a result, the springs had to be spread to install on the rear. When fully loaded, the spring flattened somewhat resulting in the shackles being under tension from both the vertical weight of the car and the spring pulling in horizontally and this resulted in the shackles being at about a 45º angle. In '42, the perches on the rear were pulled in and the spring length was adjusted so that under load, the spring end to end matched the perch to perch on the rear and the shackles hung straight down. Thus, the shackles did not give any horizontal stability to the frame and body. So, they installed a Panhard bar which was attached to the frame on one side and ran horizontally across the car to attach to the rear (adjacent to the perch mount) on the other side.
So, what does this mean? Unless you want to add a Panhard bar, the '48 spring / '48 rear perch arrangement is not an acceptable option. (Don't ask how I know.) The one year only '41 set up has the same perch to perch as the later years and the unique to '41 spring gives the 45º shackle angle. But, the spring is hard to locate. Also, the '42 through '48 spring has very large diameter eyes at the ends requiring the special later shackles.
