If you want to swap the entire rear axle the 57 to 72 F-100 9 inch is as close to bolt in as it gets. It looks like a 9 inch under your stock truck though...
A better option in my opinion is to get the 3.54 ratio gear set from a 51 Mercury, part number 1M 4209-E. This should bolt right into your axle. This website has a listing for one:
http://www.vapinc.com/ringandpinions/main.html