I AM DOING A DISC BRAKE SET UP ON A 1970 CHALLENGER I AM USING 73 A-BODY SPINDLES AND NEW CAPLIPERS AND ROTORS I LIKE TO KNOW IF THERE WILL BE ANY PROBLEMS WITH THIS SET UP.

Should bolt right on there. Basically that is just putting a '73 E body disc setup onto the earlier E body.

Exactly the set-up you need,

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

As said a bolt on deal & check (hose routing/location). On your '70 if the hard line locating tab if it is in front or behind the spindle as F body calipers MAY have a more advantageous hose mounting location on the caliper than A body ones for the best hose routing. Get an idea of what you need & have your parts house set out both of em to compare. EDIT and related to hose routing, the spindles/calipers can be switched for side to side. Mock everything up & get the best fit you can.

CAN I CHANGE THE A-BODY SPINDLES AROUND SO THE CALIPER ARE MOUNTED IN THE BACK INSTEAD OF THE FRONT OR CAN I GET STEEL BRAID LINES.