Think I used washers with mine. Caught the edge of the metal tab under the edge of one of the screws. Sounds "ghetto" but once it's in, it isn't going anywhere.
I think I left the post on the back of mine. I certainly didn't have to remove the bracket from the front edge of the console.
find that all the wiring harness/adapters seemed to get in the way. Made it hard to push the radio into place.
88 Formula IMSA Fastback. 4.9, NVG T550
Praise the Lowered!