Is your bed 97" or 89"? inside length? After 55 second series, the 1/2 ton and 3/4 ton long beds are the same. Long beds became 97" inside in the 57 model year. If your bed is 97", it is longer than the frame and will be difficult to connect at the rear frame horns. Your frame is a couple inches wider than the 55 second series, but that should not be much of a problem. We did an article on bed changes year by year.
http://www.mar-k.com/installation_hints.html that may be helpful. Scroll down to "Bedside Interchangeability". This is not a simple bolt on swap, but is can be done depending on how original you want it to look. There is a lot different between 55 first and second series beds.
Mar-Ktech
