...Notice how this right side Magnesium Center-Lube Cam Cover has 9 mounting stud holes (one behind the oil-line). Now, take a look at this other http://www.pbase.com/9146gt/image/35390328 Magnesium Center-Lube Cam Covers and note how it has 10 mounting stud holes. Additionally, notice how the threaded hole for the center-lube cam oil-line is oriented horizontally on this cover and vertically on this cover http://www.pbase.com/9146gt/image/35390328.

Why the difference you ask?

I believe that the ones pictured here http://www.pbase.com/9146gt/image/31433118 seem to be for the early 906 chain housings, I didn't know the Porsche factory also made them available in Magnesium. These would fit what I would call the Aluminum engines, 1964 thru 1968. The later style had more studs (sort of like the later exhaust valve covers which were predominantly made from Magnesium, 1969 thru 1977). At least that's they way I understand it, it will be interesting to know what Carl Thompson has to say about them. I'll ask and update these comments appropriately...