installing Alpine in Nissan Terrano

Anyone have experience of installing an Alpine CD / radio into a Nissan
Terrano? Problem is the two L-shaped brackets which Terrano has- the two
holes in the brackets don't match screw holes in the sides of the CD player.
As the area behind the dash is huge, cavernous and empty (except for the two
brackets), what is the recommended method for fixing the unit in? At the
moment I have the unit attached by one screw on each side- and the fascia is
stopping it from tilting backwards into the hole.
Hope you can help!

Paul D.