Yep, thanks alot! Now I can see what you were talking about... I did the stupid mistake to assume the studs should have been originally perfectly centered, and that those in the heads that I was measuring were bent...
It's funny that by the looks of it, the #1 stud pattern isn't at least a mirrored image of the #2... I wonder if there's any logic reason why VW did them this way...
Anyway, this will make it a bit harder, as I wanted to make these by exact measurements, in order to fit them to any heads, and not only mine. That's why I had the holes drilled by CNC, not to induce any human error. Now I'm in the dark, and the best I can do, is to take an old heat exchanger like you did, and copy the pattern from that... but I'm not convinced yet.
I kept searching for original measurements/drawings but all I could find is these 2 pictures from our fellow member dd-ardwark (David?)
http://rides.webshots.com/album/576679922NkjsGf
And a few figures on Richard Atwell's website, but nothing too helpful.
http://www.ratwell.com/technical/Exhaust.html