toshi:
The two threads Dave mentioned cover a lot that I won't have to repeat here.
I'd only suggest to be VERY careful in adjusting your heights. You MUST understand ALEMBIC's mounting system, or you can crack the pickup shells ( see 398/3098 ).
As for the suggested heights for your G & L:
These are the heights that G+L uses in their final set-up at the factory. This is a 'can't go wrong with this' measurement to suit the vast majority of their players. Bear in mind that this is dependent on the final setup: You'd have to do these measurement AFTER the setup
(nut, neck relief, neck tilt, string height over the last fret, bridge saddle heights)
is complete.
Of course, put them where you want them to fine tune your sound. You may want to fine tune the threaded polepiece adjustments to match output string to string, if your ears can hear any difference. The polepiece heights adjust in just fractions of one turn, so don't get carried away.
There really is no technically 'right' height for pickups. It all just depends if you want a little
cooler, open sound (lower in the body) or a hotter, firmer tone (closer to the strings). It's your call. As I said, the factory heights are a best-guestimate for the majority of players who will never experiment with this.
J o e y