Whoa guys! We're mixing my first two paragraphs about how changes in calipers etc can effect a system (side topic) with the rest of my post about the possibility that the bore of the OP's master cylinder could be the cause of his problems. All the bore diameters listed in the second part of my post refer specifically to the pistons in the Master Cylinders.

As far as the calipers go, I do agree that IF we were going to be considering a swap from a 4 piston Bendix caliper to Cordoba caliper, we'ld want to consider fluid at displacement. Now as far as force goes; If the MC stayed the same and the amount of force applied to the brake pedal stayed the same, the pressure applied to the front brakes would stay the same, athough there would be less pedal travel.
Then at the calipers, we have to reverse the calculation to figure the force applied to the pads.
The force on one pad using Bendix calipers is 6.3 sq. in. x Pressure.
The force on one pad using a Cordoba caliper with a piston of 6 sq. in x Pressure.
Not quite the same, but in the same ballpark. At say 500 psi the Bendix would be applying 3150 pounds force and the Cordoba pad would be getting 3000 pounds force.
A more complete braking force comparison should also consider effective radius and swept area...
I also agree that drum to disk is a very different animal to calculate and fortunately we don't need to do that here!