master cyl. for pwr.disc brakes

now have manual disc brakes on 340 demon. stock motor. my m/c now has
1 sq. port & 1 rect. port. want to put pwr. brks. on. picked up a used booster
& bought a pwr. m/c at the local parts store. the new m/c has 2 sqare ports.
they claim this is what the book calls for. anyone have an orig. pwr. brake car
to confirm the right m/c i need? thanks.
jerry