F-3H-3 or F-3E, Demon II
Here's a what iffer, What if the Demon got a proper engine, say a J-67 or j79, also with the upgrade is an IR sensor under the nose, duel wheel nose gear,zero-zero ejection seat, fully enclosed IFR probe, F-4 style stabilators, slap on a pair of F-4 wing pylons with LAU-7 missile launchers. With these improvements there might have been some still around in the early days in the Tonkin Gulf or Yankee Station. May be taking on some Migs. The kit is the old Emher with bits from the spares box as are the decals.
The actual Demon suffered from a poor engine choice,the notorious J-40, The replacement engine J-71 was an improvement but had it's own set of problems. a change in mission requirement also prolonged production delays.