The requisite hardware for stepping up from Stage 1.
You can now use EITHER pulley to attain basic Stage 2 power levels, or BOTH pulleys to maximize power before the final step, which is the UltraCharger.
Use of either or both pulleys will require an APR Stage 2 ECU upgrade ($249.99), which can only be performed at an authorized APR dealer, like RocEuro.
A new belt is required for each layout.
Make note that the APR Heat Exchanger is recommended to hit advertised power levels when running Dual Pulley or UltraCharger.
If you're looking to do the single pulley upgrade, just do the SuperCharger pulley, as the labor is less involved. If you're looking to do the crank pulley, or both pulleys, consider that the heat exchanger install requires the same amount of labor. Save, and do them at the same time!
Quick References - Max HP, 93oct
Stage 1: 444hp/372tq
Stage 2 Single Pulley: 458hp/387tq
Stage 2 Dual Pulley: 468hp/432tq
Stage 2+ UltraCharger: 498hp/444tq