Not quite correct. There is no conversion kit from a viscous transfer case (HF2AV) from a fzj80 to part time. The kit is for a non-ABS vehicle with HF2A transfer case, which generally means '91 and '92.

If you want to convert an ABS fzj80 to part time, swap to a non-viscous transfer case, make the conversion to part time, install manual hubs, and install the center diff lock switch. Not an economical modification IMO.

Edit:
Saving 5MPG due to a part-time conversion is not realistic. Those comments were from one highway trip. IMO you would net about 2MPG average.