I found this on the web few weeks ago. Here we go:

http://forums.audiworld.com/v8/msgs/66322.phtml

http://www.928oc.org/dcforum/DCForumID9/23.html

The O-ring size they used are:

Fuel Distributor Base O-Ring (1 required)
– 35mm ID X 39mm OD x 2 mm thick

Piston Cylinder Housing (1 required)
– 22mm ID x 26mm OD x 2 mm thick

Cylinder Housing Nozzles (8 required)
– 8mm ID x 12 mm OD x 2mm thick