The code on the door sticker is easiest for sure, anymore I just google ranger axle code to find the list, less buttons, the TRS link is one of the top ones...
The axle tag will have two rows of text, ignore the top line, the second line is the important info and 90% of the time the first digit is under the bolt head but like Eric said it will read 4 10 (no period) or 4L10 (or 3 45 or 3 55 or 3 73 or 3 08 or 3 27, that's all of the factory ratios).
That said, both trucks have the same front axle too so you can swap the front axle with the rear and be safe either way. It has nothing to do with the transfer case, there's only been 2 transfer cases from 1983 to 2011 with a few small changes over the years but all are either a Borg Warner 13-50 or Borg Warner 13-54, both of yours have a CV joint front output so are the same version of the 13-54.