I assume you mean an FJ62? Most markets the FJ60 was replaced with a carbuarated version of the 3F which made it an FJ62. North America had a 2F FJ60 until 8/87 when a fuel injection 3F was introduced as the 3FE.
I have owned my 89 FJ62 since 1993 and kicked around the idea of a H55F five speed conversion. Probably just keep the auto. Got use to it being a slug on the highway. If I were to do a 3FE in an earlier model would be with a H55F. May do a llittle in a lighter vehicle with the auto but would lose some of the comforts of the FJ62. If I owned a nice FJ55 would not modify anything that could easily be undone. If I didn't have a nice FJ62 I would go to the effort of the auto when it would be as nice a driver as the FJ62 was right from the factory
At one point I had 33" tires and a 2" lift on my FJ62. Going from 1,100' elevation to 7,000" on weekends it was a real dog. I switched to 235s only because I couldn't find 225 the standard size in light truck only passenger tires. The vehicle now lives and 7,000' and run 31s. I still on occasion use the shifter to keep it in lower gears on hill climbs. If my 62 was a DD would seriously consider the five speed.