You're unnecessarily trying to over-engineer the brakes. Seriously. One good brake setup from a motorcycle would provide more stopping power than you'd need. As for the Jeep parts, no need for the freaky-deaky plumbing. Run a line from the front reservoir to the caliper. Leave the other side dry and plug it. If the reservoirs aren't "seperate" enough, you may have to remove the residual valve from the rear side of the master cylinder before plumbing the outlets together. This is based on the assumption that the Jeep had rear drum brakes. If it had rear discs, ignore that bit. No vac booster required. As for sensitivity, it's a matter of leverage. Changing the amount of leverage your pedal has on the master cylinder will alter the sensitivity. If brakes are too sensitive, increase the physical distance between the pedal's pivot, and the plunger point on the pedal. This will also shorten the distance between the plunger and the pedal pad. To make braking more sensitive, reverse this.
Comparison point- My kart weighs about 450 with me on it (about 300lbs, kart only). My master cylinder is the clutch master cylinder from a Toyota pickup truck. The caliper is from a '70's Mercedes. At a (current) maximum speed of 45MPH, I can easily lay a pair of black stripes on the pavement when I hit that pedal. Pedal effort is easy, without being retardedly sensitive.
