The Stainless Steel Brakes caliper A185S is the best bolt-in replacement. Piston area is close to the original, and so doesn't require a master cylinder change. Because the piston centers are further out on the disc surface, there's 5-10% more mechanical advantage.
http://www.summitracing.com/parts/ssb-a185-s
*By the way... Before you do anything, check that your brake balance bar is set up correctly. If you don't have enough stroke-bias to the front master cylinder, the balance will be off and the pedal will be really hard.
In addition, the pads can become glazed when they are not used hard during the break-in, or for a long period afterward. If sanding the friction surface doesn't fix that, replacement may be necessary.