here's a thread about it on the Samba:
http://www.thesamba.com/vw/forum/archive/index.php/o-t--t-321343--.html
One rekons he was able to do a straight swap with a 12v Porsche 912 style generator.
QUOTE:
"The Porsche GR26X generator, you should use the normal VW 6V backing plate/tin, and pulley. I'm not sure about the dimensions of the Porsche parts, if they are the same as the 6V VW then yes you can use them. Don't use 12V pulley or tin.
Voltage regulator, when I had that setup in my 62 bug I used the one that Bosch sold to match it, the 0190350049, which was rated at 25A. I've always kind of wondered about the 38A stamp on the GR26X generator, I don't really think that can be right, the Bus 12V generator rated 38A was larger than the normal 30A one.
What regulator would I use, well, the 0190350049 I mentioned above, plus I'd bet the new solid state/electronic 30A regulator would probably work fine as well.
Again, points/condensor, will work fine under 6V or 12V.
-Andy"