Hey Skyflash
Hope I'm not too late to be of assistance,
I'ts EASY-----
Just route the main hole for the trem, but a little bit deeper,
say, about 3/16", (the thickness of the trem body/plate) depending on
how low you have to go.
Then sit the trem in position and draw around with a pencil
and there's your routing guide !!!!!!
That's how I did mine about 15 years ago, worked fine, and still working !!!!
The top of the trem body/plate is set flush to the top of the guitar.
I had to do this because I had set the neck in my new guitar with
too-little angle, and didn't want to CUT the neck off and start again !!!!!
(Go here to see me with this guitar: http://www.tagworld.com/iondrive )
Cheers
green_axeman
(Australia)