I am not sure if my data is correct but here I go anyways:
The Holzapfel engine is based on the T4 with 993 heads with EFI.
Pics are in the engine gallery. Dr Gerold's Race Super has the engine in the back. In race trim the engine produces 280hp for the street I believe it was about 250hp. This is a NA engine.
Pics are in the gallery here at Germanlook
....where else:
http://www.germanlook.com/Functions/...mages/0064.jpg
http://www.germanlook.com/Functions/...mages/0065.jpg
Another option would be a 2.6-2.8 T4 with Apfelbeck heads (pic in the engine gallery) ...if you find them. Two T4s with them reached the 100hp per liter mark. Those are the only T4s that had those heads as far as I know.
Alex