I bet that axle is going to be somewhat too wide, even for a flatbed. Measure the track widths to see how different it is.
My dad bought an '88 light 3/4-ton 4x4 brand new, then passed it on to me several years ago. I've since sold it - the vehicle was always something of a lemon, blowing up a couple of transmissions and transfer cases, along with numerous sections of the electrical system, within less than 100k miles of mostly garaged and very well-maintained service. My personal opinion would be to find a better starting point for conversion parts.
