Suggested reading - Mopar Action disc brake write-ups. Link below. The way I read it the 70-71E disc setup will work if you change everything including ball joints and upper control arms from the donor vehicle. The 70-71 E disk set setup is expensive to service - check prices for replacement rotors. The late A body setup - including spindles and upper control arms - is the best with factory parts.

There may be some tricks to make your swap work easier... bearing spacers ect. If you are starting with 9" drums though, the whole setup should be changed as the 9" spindle/balljoint setup is not up to performance work.

http://www.moparaction.com/Tech/archive/disc-main.html