If you happen to have the Porsche PET parts diagrams, take a look at the crankshaft diagram and you'll see that pulleys #12 (single pulley for just the fan) and #12A (double pulley for fan and A/C) both use the same bolt #15 that is M12 x 1.5 x 22
Note that this bolt can be a bear to remove. It's got a serrated surface underneath the bolt head and it bites into the pulley surface VERY well. I recall some discussions about this in the past and then the thread was resurrected a few years ago when someone asked about the torque for the Rothsport aluminum pulley install.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/163214-crank-pulley-bolt-washer-no-washer.html