Proportioning Valve

I recently switched my car (69 cuda) from front drums to disc. I bleed the lines, but still might have some air in the lines, but not positive. My pedal still feels a little on the "weak" side. I still have the factory Distribution block. I know I should change it out for a proportioning valve, but would that make the pedal feel soft? Also where is a good place to get a proportioning valve that will mount in the distribution block location?