Does anyone know where I can find a reasonably priced Disc Brake Conversion kit for a 1965 Dodge Dart 270 6cyl. And also do you have to change the upper a arms?

Just swap the brakes from a later model A body on there. Lots of ways to go depending on if you want big bolt pattern wheels or 15 inch wheels so you can run the larger 11.75 rotors etc. You can put the small bolt pattern disc brakes on there too if you want to stay small bolt pattern.

a set of Kelsey Hayes SBP A body discs would keep you SBP or a set of 73-76 A body (Ebody might be the same also) BBP discs if you want BBP & they increase the track some & you would need the UCA from the disc donor car (if getting them from an A body, E body UCA'S would not work). with them you would want to get rebuilt calipers from a '76 A body for the larger (2.75") bore and brake hoses from a 78 volare (just cut half of the bracket off that is crimped on in the middle of the hose). I think Doc has a tapered spacer sleeve (need 2) that would let you use your current UCA's with 73-76 discs