Anyone who wants to reduce spongyiness/travel a bit, I'd get rid of the 5/16 rubber pad that is inside the booster, under the booster rod.
old article but have been thinking of doing this upgrade and buying the parts piecemeal.
Its my understanding that all you need is the 6 piston brembo from a 13-14 GT500, the 15 inch rotor and the brake lines.
First time in researching this about possible replacing and upgrading the master cyclinder