Hi Michel
I have your email but with you making the title of the thread accurately I thought I might answer here so everybody can see what the best way is to proceed.
You have to machine the caliper carriers already attached to the RS6 / RS4 calipers, that then centres the disc in the caliper.
In addition the centre bore of the Audi disc is 68mm where you need 65mm on the golf so you need a very thin spigot ring manufacturing which also reflects a small radius on its lower side so it fits correctly, in addition you will also need a specially machined expanding collet as the RS6 disc has no mounting hole we have to create one. And finally you also need to reverse the calipers from leading to lagging by reversing the connecting pipes, this can go very easily or it can be a nightmare and you have a pair of written off calipers on your hands.
Its all doable - I have the mounting parts either in stock or the drawings for them, we have a drawing for the carrier machining.
Problem being I am guessing you are not in the UK.
I would also warn you that the discs are never very easily transferred and nearly always are warped or damaged which is why they were the ebay bargain in the first place.
Contact Illektronic on here he's got them fitted on his GTI heres a pic for inspiration:
Just edited to say the total piston surface area of the RS4/RS6/R8 calipers is 60 square centimetres thats about 20% over optimal which is around 49 sq cm, that is a lot but Im guessing they'll be more decorative than Nurburgring! Tony D's description of the pedal is accurate