disc brakes on a duster

got my brakes all together. went to bleed them and had no pedal after i got all the air out. i bled at the master cylinder and at the wheels. so i went and got a different master cylinder. i originally had a manual drum mas cyl on my 72 duster. so i went and got a manual mas cyl for disc from a 73 duster. it helped alittle. but ive bled at the mas cyl and at the wheels and there is still not much of a pedal. it takes several pumps to get a good pedal. i know that there is a possibility that air is trapped in there but i was wondering if my brake pushrod is the wrong length. the pedal goes most of the way down before it has any resistence. any ideas?

thanks.