Just did this the other day.  I used a
dremel tool to slice through the bit of
green plastic that held the backside part
of the assy together (you cant remove it
through the front of the dash w/o destroying
it as far as I could tell?)   Maybe there is
a trick to this, but I was careful and it seemed
to work.  Plus I got to use my 'rarely used'
high dollar dremel! :-)

At any rate.. I put one of these in...

http://tinyurl.com/3scd9k

Be sure and disconnect the battery
prior to doing this, you dont want to
fry anything else connected to that
circuit (clock, radio etc: )

hope this helps

 -tim

90 syncro westy
gilbert, az
http://www.timschneider.org