Here's the deal with mounting a head unit into a dsm. If you have the single did radio, with the pocket below, you're in great shape. If you have the double did radio, you will have to get the kit, or I would recommend getting a pocket at a local dealer or bone yard.

Pull the factory h/u and iso-mount the radio into the factory brackets. On Alpines, you will want to pull the bracket with the pins off of it first. It takes a #1 Phillips head screwdriver. Once that is done, reinstall the headunit, without the trim ring. Put the bezel around the radio and pocket and then put the radio trim ring back on the alpine. This will give you a nice look.

If you need to use the kit, the same pretty much applies, but it will not look as good as using the factory pocket.

As far as depth, we have plenty of room behind the headunit.

Good luck to you!