Yeah I thought of something like that too. In this world, the F-4 Phantom never gets built, so the US Air Force finds itself short of a dogfighter to counter the North Vietnamese MiG-21s et al. They eventually select a licence-built Mirage III: Vought would be the likely US partner since they had a technology transfer agreement with Dassault in real life. The first version is a straight copy for speed, but they then work the design over, adding fixed canards for maneuverability and a J-79 for p/w ratio resulting in a hauntingly familiar aircraft: basically a Kfir with a radar nose....
An Avon-Mirage was seriously offered to the RAAF: how about one for the RAF with AI.23 and Red Tops? It could be a joint development between a less anglophobic Dassault and Fairey, the intention being to provide something cheaper and more exportable than the Lightning.