Did you ever get your brakes bled? I replaced the MC on my '87 Sport the other day and had the same trouble as you. I tried bleeding it half a dozen times. I tried using my brake bleeder and doing it the old fashioned way and could not get any pedal. I finally had to take it to a garage and let my mechanic buddy bleed it for a couple hours before we finally got enough pedal to make it safe to drive on the road.
I ended up getting another master cylinder. I bled everything the same way as before and the pedal is definitely better but it's still not perfect. The car isn't running so I decided to leave it so I could start on other tasks. Once the car is running I'll mess with it some more. I have plans to make braces for the MC and brake pedal assembly to eliminate the flexing going on to improve the pedal feel.