66 Barracuda A/C vent to dash dimension

Anyone by chance have the dimensions for the mounting bolt spacing for an under dash A/C vent? I'm replacing the original dash that was cut up for a radio/cassette player with a 66 non A/C dash with the correct radio which does not have the bolts mounted (see photo). There are 3 lips on top of the vent which I'm sure butts up against the underside of the dash (see photo). I know I can get close fitting it up but dimensions always help, especially when your drilling holes. Would any other support be necessary?

Thanks

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