"It never happened" leads to a couple of interesting ideas, a production F8U-3 and/or an enlarged F5D variant with a J75 and variable inlets (I'm partial to Fieri inlets like the F-105's myself). Choice of seats (tandem for a two-seater most likely) would be up to the modeler and backstory.
And that's just for the Navy. What might the airforce had done for Vietnam once they realised they needed a dogfighter and they were losing Thuds hand-over-fist?
1. Productionised F-107 with the intake back in the ventral position?
2. F-106 "gunfighter" (Vulcan plus fuel in the bay, twin sidewinders on new outer-wing pylons) deployed to 'Nam and the production run extended?
3. Fighter F-105 with a bigger wing, fuel in the bay and more missiles? (for all their size, Thud's did surprisingly well in air-to-air combat: most of the losses were down to ground fire, and many might have been avoided by better detail design)
4. USAF procurement of the F-8 Crusader, possibly with a J-79 and a Vulcan?
5. USAF emergency procurement of a foreign type? A J-79-engined Mirage would seem tasty, and might, of course, give other people ideas......