You can not use the rotors from your IFS but you can use the calipers, the vented rotors you need are from a land cruiser, and you may not even need spacers, it just depend on the backspacing on you wheels.
Some good info taken from the Pirate4X4 Toyota FAQ
"Brake Rotor Swap – Vented Front
Some folks like to swap out their solid rotors for vented rotors. This is a simple and somewhat inexpensive modification. I did this swap because my brakes were getting very hot and making some very annoying noises. If you can change your brakes you should not have any problem with this swap.
79-80 toyota mini axles -> Rotor bolts onto hub with 6 bolts and the wheel studs are pressed into the hub only. For Land Cruiser vented brake swap you must use 79-80 LC rotors.
81-85 toyota mini axles -> Rotor bolts onto the hub with 2 bolts and the wheel studs are prasses through the hub and is pressed into the rotor. For the Land Cruiser vented rotor swap you must use 81+ LC rotors. Uses Toyota 90942-02053, Dorman #610-264 or Napa 641-3126 wheel studs.
The Landcruiser rotors are wider because they are vented but otherwise fit right on with no other modification besides the need to run a IFS caliper.
The caliper comes in two flavors... one has two larger pistons and two smaller, and another has four pistons that are the same size. The ones with four large pistons would technically give you more braking force. I used the same pads because mine were still fairly new... so you don't need new pads unless yours are low."