1967 Dodge Dart Radio installing
You don't need to hack up a "donor dash frame" Just take some sheet metal and make a plate for the radio to fit, and mount that behind the dash with small screws, in positions which will be hid by the bezel. You might have to make clearance dimples in the back of the bezel to clear those screw heads. Pop rivets might be better, tack welds, etc could also be used.
You've got the bezel, that gives you "location."
Make whatever you have to for a support strap for the rear of the radio. Here we call it "plumber's tape........"