If you're using the silver palmrest from the G3 as well, you'll need to use a bit of fine-grit sandpaper along the inside edges where it fits around the magnesium frame when assembled, as the G4's frame is just slightly larger... at first, it seems as if it will fit, albeit snugly. I found out the hard way when the heat from my hard drive caused a crack in the left palmrest, starting from the lower left corner, moving inward toward the keyboard. Of course, I was using a 5400rpm Seagate, which tends to churn out a lot of heat... more than the newer 7200rpm model I have in my MacBook, so the newer ones may run cooler. But, I would still add a little clearance room, and I would use sandpaper, as a Dremel is going to remove too much too quickly for something like this, where you want to remove barely anything at all
-the added clearance should be less than half a millimeter on all sides.