Bad Master Cylinder or Air?

I received the new master cylinder on Friday and got it painted, bench bleed, installed on car and than bleed each wheel several times. Pedal felt a little better but was still soft. Back when I first starting messing with this issue I took my the brake rod off my 1975 Duster to measure since it has factory disc, etc. It measured 1/8" longer than the one on my Cuda. Lots of people say that the manual rods are all the same or work.. I figured being only 1/8" shorter it should be okay, just was the variance in production lines back in the day or they changed them a little bit from 69 to 75. Anyways I bought a adjustable rod when I got the 2nd new master cylinder just in case to try. Well I adjusted the new master cylinder rod to the same length as the one in my Duster and now the pedal feels like it should. I took the car just for a trip out the driveway and back (I have a LONG driveway) and I am now able to lock up the wheels. I would never of thought the 1/8" difference would've made that much difference, but it sure did.