Hy ratamugrosa, I think that the seven inch booster should work, you are restricted to size by the clearance at the mounting bracket supplied with the kit. There are some boosters available that are a double diaphragm type, which provide more boost, check with the supplier. Make sure you have all your brakes adjusted up properly before you start bleeding your new systems, don't forget to bench bleed your new dual master cylinder before you install it, hope that helps.
