I'll be doing this swap on my Murple S8 as soon as it needs brakes or upper suspension arms. Its mechanically easy, but sourcing the parts is very difficult as the spindles / uprights are extremely rare now. I've bought whole A8s just for the front uprights
D3 A8 brakes are pretty thin on the ground too, although Phaeton bits are easier to get and a lot cheaper. D3 S8 brakes are almost impossible to find.