As far as I am aware the front wishbones fit the rear physical dimensions but the correct rear wishbones do not have an anti roll bar mount union fitted to them, they can be fitted upside down, look at the pressings in the wishbone for correct way up, been down the garage and found front and rear wishbones, photo below of near side wishbones front and rear, front wishbone has red circle with anti roll bar bush, green circle has bottom ball joint in it bending forward, notice rear wishbone, no welded in union for anti roll bar bush.
Photo below of under side of both wishbones, notice the pressing in the blue circle, I think this to let water drain out. sorry don't have a bottom ball joint link arm for rear wishbone but had a look below Ur quattro and it bends to the rear, more advice as if you need it, take photos of every thing as you dissemble it, yes it is a pain to do but if you take photos reassembling you will have before and after photos to post on the forum.
