I think that is his plan Robin, but there are undoubtedly going to be issues with the bell housings, ECU, all engine plumbing as well.
It would be easier to completely strip the entire engine/loom/ecu/clocks out and replace with the items from an S3. As then, you will at least have the necessary gearbox/transfer box that will mate up to the haldex 4wd system, but the clocks wouldnt fit most likely, so a genius would be required on that side of things to bypass the security with the standard R clocks.
Although, i have to admit, its a totally pointless excercise. It would be cheaper just buying an S3 and selling the R or even super/turbo charging the R.