The Lexus LS400 brake calipers (1995-2000 models) are more powerful 4-piston calipers that are also lightweight compared to stock sc300/sc400 and mkiv Supra NA calipers. They stop these cars a lot better, were designed to stop the ls400 cars from 150pmh to ZERO mph, and are easy to install. Here is how I did mine:
1) Remove your wheels and lug nuts
2) Our Brake Calipers are held in place by TWO 17mm bolts. Unscrew these and the brake caliper is now loose and slides off the brake rotor (aka disc). Since the lug nuts are off and you've just removed the brake caliper, there is nothing securing the brake rotor (aka disc) in place. So, slide the brake rotor off the wheel studs and replace it with a LS400 brake rotor.
3) Put the wheel lug-nuts on and hand tighten to keep the new LS400 brake rotor steady & secure.
4) Make sure you Hammered/Bent/Cut parts of the sc300 brake dust shield to fit the LS400 brake calipers & rotors.
5) Place LS400 calipers on the rotor and align the TWO mounting holes. Install TWO LS400 17mm Brake Caliper bolts (shorter than sc300 ones) and torque them to 87 ft/lbs of torque.
6) Disconnect your stock brake lines from the sc300 brake caliper (2-piston inferior design) and screw that same bolt-brake line into your LS400 calipers = very simple. You're just plugging the same brake line, that was in the sc300 caliper, into the LS400 caliper.
7) Bleed your brakes properly!