Listen to Terry, he just did exactly this for me, 99 cougar returnless atx into a 96 contour mtx.

Oh and if you decide this is more of a project than you can handle, Rockford isn't a bad drive at all. (In other words HMS has my recomendation)

Geoff C. Turner

99 Black SVT -mine
99 Blue SE V6 ATX -mom's
96 Black SE MTX -sister's