Yep, rear fenders fit from 53 through the end of step side trucks in the mid 80s, there was an optional left rear fender with a cut out for mounting a spair on the box side. The top rail went from a 45 degree angle to 90 degrees in 57. After 57, a step side box was either a 7 1/2' or a 9' box, but all were the same except the length.
Dodge trucks used the beam axle through 71 model year with a big block option from about 67 or 68 on, The newer upgraded drum brakes bolt on to your axle. If you want disc brakes, I think
www.rustyhope.com makes a kit to convert to discs. A lot of guys are clipping the 50s trucks with Dakota clips, and some are using the entire Dakota frame. Saying what is best depends on what you want. Gene