I am switching my 69 Dart over to 74 Duster disk brakes and need to get a master cylinder. I would like to get a more modern MC rather than the type which would have came on the 74 Duster. Any recommendations? Could I use a MC from a late model Mopar like a Dakota for example?

It really depends on whether you decide to use a power booster or not. A stock 73-76 power booster and master cylinder is really hard to improve upon. The factory NON power master cylinder is a very close second. The power setup will place the brake pedal closer to the floor, which I like. The manual setup sits so high up, its as if your knee wants to hit the backside of the steering wheel when lifting from the throttle to press the brake pedal!
Anything modern will likely have a 2 bolt mounting flange, requiring the use of a commonly available adapter. Dr Diff and The Ram Man are Moparts members that should be able to help.

DoctorDiff can supply you with all the parts. Best bet is the new style aluminum master cylinder. Eberg also sells them on e-bay and maybe on here in the parts for sale section.

I emailed Rick E. last week to ask about the aluminum m/c's and he said they're long gone Should have ordered one while I had the chance!

Dr Diff supplied mine. Smaller bore so it requires less pedal presure. I had to add an adjustable rod to get the pedal up where I wanted it. He is great to work with!!