I just did a similar install in mine. Although I had a cut up hole in the front of my dash already, so I cleaned it up and put the deck there. I mounted the same style dual voice coil speaker in the dash grill area, also.
A retrosound 6.5” round fits perfect and uses the original mounting location, which is THROUGH the slats in the dash “grill”. I used all black hardware there, but did use the same finishing washers you did. Nice work.