The RS4 3 Evo+ diffs are a direct bolt in. These are hardened diffs and they also have a higher ratio...
I use these on my RS4 super rallys which were originally nitro mt1s. I am also running the velineon vxl 3s systems in it with 3s 35c lipos.. They run fast and I have no issues with the diffs. I picked the up from a chop shop on the bay fully assembled and they dropped right in..