I have 81 FJ rotors on mine with the V6 calipers as well (still using the SA hubs also)  .    FYI, the four cylinder calipers have two small and two large pistons in them and the V6 (maybe turbos also, not sure) calipers have four large pistons and more/larger external cooling fins.  Because of the cooling fins on the V6 calipers you'll have to check for the fit of your wheels since they may hit the fins on the calipers once bolted up to the hub and may require wheel spacers. Not all wheels will give you this problem, mine don't  .