I sortof don't get the point of this? The v8 one I totally get - it's essentially the z8 coupe that never was. The s54, albeit modified, is just a Z4m coupe with the wick turned up a bit and a different frock on for a load more money? You can 3.4 an s54 with hack engineering for about 12k iirc...
As others have said, if a restomod was on the cards, an Alfaholics GTA or Tuthill 991K would be where I'd be going!