I've recently installed new brakes wheel cylinders and lines on my 72 Duster.My question is,since there is no fluid in the system should I mount the new master cylinder and fill the system before I bench bleed the new master cylinder?I am not sure if this would minimize the chance of getting air back into the master cylinder.Any thoughts?

I kinda confused at what you said there but bench bleed the master first, then the system.

Bench bleed then install. Either way the entire system needs bled. Start with the rear pass then rear driver then front pass finishing with the front drivers side wheel.

That help?

If it were me, I'd probably bench bleed the master, open the bleeders in each corner, hook up the lines, and let it gravity bleed until you get fluid at each corner. Just don't let the master run dry. Then you can bleed as you would normally.

The clean way to do it.... Get yourself a short length of 3/16 vacuum hose & an oil squirt can, make absolutely sure the oil can is clean.. I have one I use for this that never has anything but brake fluid in it.. They are easy to disassemble & clean, I suggest you do that... Fill it with brake fluid... Completely assemble your brake system then starting with the right rear loosen the bleeder screw & using the oil can push fluid back throught the brake line.. Doing it this way the first line only needs fluid pushed back to the T... Then move to the left rear & again push fluid back through the line but this time Your pushing it back till the master cylinder is maybe 1/4 full... Go to right front & repeat but this time your again wanting to raise the fluid level in the master slightly .. Then move to the left front & repeat....

Speed bleeders help also.....

correct.....I was just throwing them in the post because they're niffty !