These adapter brackets enable you to fit Lexus 4 pot calipers, (ADVICS) from IS350, RC350 and many other models. They have 334mm rotors which makes them larger than Supra big brakes. They are very common now and can be bought for as little as AUD200.00 a pair from an auto wreckers.
 
The brackets are made from mild steel for strength and the bolts are high tensile.