Factory Radio mount questions on a 66

[msg]

The radio I wanted to put what I thought was a stock radio for a 66 but its not lining up. I am trying to get it mounted for fitting and design a bracing strap to support it from behind, but when I try to mount it up the right side isnt flush enough to thread a nut on the front to fasten it. The left side looks flush, if I can find the nut to thread on it. There is one on there but I think its the nut holding the dial to the unit and shouldnt be loosened. I think its a 7/16-20 but I couldnt find one at the parts store thats thin like that.

Is there a way to get this radio mounted up?
What parts should I get to mount this right to the front dash?