Brake size

At this point I would be looking at application..

Fronts...

69 Dart if it was originally a V8 car 10", if it was a slant 6 car 9"

Rear...

Look at 74 dart V8 car 8.25 axle 10", the only other option is 7 1/4" rear.

Look at the available shoe sizes. That will tell you a lot

Look at the rear for obvious signs of modification like spring perch relocation.

If it looks stock then the 74 is a good bet.