I am having brake issue on my 1970 duster

I agree with @Dana67Dart, we need more information. There are several things that could be going on. Do you still have the old master cylinder (MC)? If so, compare them to make sure you got exactly the right one. If the actuating rod does not match the new MC, you likely won't have brakes. Also, were the brakes working before, and the MC failed? Then that would certainly point to the MC. How old are your hoses? You probably have three; two up front and one at the back. Those can fail internally which will cut off brake fluid flow. And my last question is, how did you bleed them. A friend of mine loves the method where you have someone pump, pump, pump the pedal and then you open the bleeder valve. I don't like that method. I don't think it works all that well. I like the method where you open the bleeder valve, the assistant presses pedal to the floor and holds it there, you close the valve, the assistant lets the pedal rise up, and then repeat. I am NOT questioning you brake bleeding ability; I just think there are good and not so good ways to bleed them.