I would like to convert the manual drum brakes to power discs on my 67 mustang 4 speed.  Is there a particular brand or company that would have a setup that would allow me to keep my new 14" Cragers?  I don't really want to replace the wheels.  

You should talk with Master Power or Stainless.  They probably have calipers that will clear 14" rims.  I have run regular 70's era single piston calipers ("Granada") with 14" Magnums and with 14" ET IV slot wheels.  Sometimes grinding on the caliper body is required for clearance.  Depends on the wheel and the caliper body casting.  

Note that in addition to the usual stuff - rotors, calipers, master cylinder and booster - you will need to replace your manual brake pedal with a pedal assy from a power brake car.  The leverage is different between the two.