Our Vanagon received a new head unit and speakers a few months ago.  Man, it
took me lots of time to get it all in with my best effort on a quality
install,  best attempt at being an engineer.

1.  I ordered speakers from Crutchfield, in large part because of the
recommendations I read here on the list and just a general good feeling I
would work with a good group.  Sure there are lower cost approaches,
but....  Thanks Loren, the Crutchfield path is a very good one.

2.  Installed a Kenwood head unit (quite old one, sitting in the garage for
some years, long story, Kenwood KDC-516S).  The depth from the manual is
162mm or 6 5/16" in.   I got it to squeeze in there.   I also got the "CD
changer to RCA plug" adapter;  and then with another $2 converter it allows
the connection of the typical iPod or in my case an Android.

It required cutting out the stock steel bracket behind the radio, I guess
the stock radio used that metal bracket for stability, which is a good idea
if practical.  I cut it with a Dremel (just trying to look good, actually
used a knock-off Black and Decker Wizard [crapppy] about 18 years old) with
those ceramic cutoff wheels.  Without that bracket it all fit so nice.
Crutchfield is great at posting all of the owner's manuals, and the manuals
have the specs, so download them and check the specs on depth, and then as
the old saying goes:  "measure twice and cut once".

Roland