Jim
I have a very similar FF conversion kit for my FJ40, and know a two of others out there, personally. I talked with the owner, think his name was Mike (couple of years ago), at Front Range, and had them machine the adapters to my spec's - made my FJ40 axle the same width as a FJ60, best price & already had the tooling for the spindle side.
It has the same components as the Front Range kit, just a different bolt pattern to attach to the housing flange, and thickness / clearances, etc.
This setup is different then the OEM 80's FF in that the "manual hub" replaces the "Nail Head" of the axle, and the axle shaft is similar to a "finish nail" wit splines at each end.
It has survived a run through the rubicon with crawler gears, etc. I do know one person who broke his axle earlier this year in the snow. Pranksters may turn your hubs on the rear axle and you just sit there, spinning,

& perplexed!
I did mine mainly because I flat tow it to certain trails, and was running out of things to do to the FJ40, but, now with the 80, hmmm!
Joe