'69 Barracuda disc brake swap using m-body brakes?

F,M and J bodies make excellent disc upgrade donors for A bodies.
Get everything from the spindles out off the F,M,J and either the upper control arms from any 73-76 A body OR Dr Diff makes a balljoint adapter. Your lower arms will be fine. You'll need lower balljoints for any 73-76 A body, drum or disc are the same BJ.