[_Ogre]

the front port is usually for the front brakes but in your application the mc is backwards so your front brakes should go to the rear port.
less fluid is used on disc brakes so you may not have much front braking using the disc/drum mc
you may be able to swap the ports and have less rear brake and then swap the lines back when you do the front disc conversion

as for the residual valve, i'd put them in. they keep a pre-load on your hydraulics thus keeping the shoes or discs closer to the rotors or drums.