I have a 2001 A6 2.7t with the standard rear brakes and 245mm x 10mm non vented rotors. I'm looking to upgrade to a larger rotor and vented. my plan was to get the 2000-2001 S4 calipers and run the stock size s4 rotors drilled and slotted and eventually go with ecs tunings stage 1 s4 rear upgraded rotors. I've also heard of people using the a6 4.2l calipers and rotors or using the 034 motor sports upgrade kit for the rears.

Has anyone on here gone with any of these options and if so was it just straight bolting on the new calipers and mounting brackets or was there any extra customizing to make things fit?