"Apprehensive"regarding rear wheel lock-up or no brakes. Still have the 4 port master cylinder & proportioning valves. Thought I was ready to add my knuckles,calipers,hoses & cables. Do I need different MC, Valves, Modifications or do these stock parts work?

 

I would imagine the master cylinder would be fine, but you may want to look into a new proportioning valve since disc brakes require more pressure to operate correctly in most circumstances.