I know how you feel, I'm doing most of this project at 2am
Mike, you have a good point. It also appears to me that the radius in the lower corners of your dash is considerably tighter. I think we are going to find quite a bit of variance car to car, depending on how much foam is in those corners, how tight the vinyl is, how wrinkly it is, how much it has shrunk etc.
The issue with the height of the supports can easily be solved by making them the short height, and the installer adding washers or something under them, moving the plate closer or farther from the dash metal until they get the fit they want in the surrounding vinyl. And yes, I think rotating them to an X and leaving out the locating lugs would allow more leeway for adjustment ( BTW Mike, how did your individual posts fit into the radio hole?)
The corner radius we have a situation where too little radius and the plate won't go in, too much and it doesn't look perfect (again based on each different car). I'd say we have to err on the too much radius side ... so at least it will physically fit into the cavity.
If it's anything like the AC vent holes in a 68 GTO dash it can be all over the place. I don't think making these padded dashes is a very exact science.
I'd bet if we had 20 good photos of radio bezels installed in Firebirds we'd see a lot of variance. It's not like we are setting up rod bearing clearance here
Couple of days and Eric should have his new plate to try out.