you can put your current 40 3rd member in the full float. I just put a full float in my 40 and put my 40 third member in it. to keep the gearing the same. you just take the block retainer bolt out of the gears slide your clips out for the 40 shafts and put it back together no clips. got 2000...
I did a sm465 in mine. took me a year trying to find a plate. ended up doing sm465 and dana 18 transfer case, with AA adapter plate. AA makes one for the 420 to FJ40 but you will end up with a tiny tiny driveline. But when I was looking i found a few places that had good info. check valley...