Paul Newman had a modified Datsun 280 ZX Turbo that he used to race in the early '80s. It had 400 hp, that car had muscle. The 280 ZX turbo was a competitor to the final C3 Corvettes at the dawn of the '80s but I wouldn't say either were muscle cars in the strict sense.
One of the few foreign cars to qualify might be the 1968-72 Mercedes 300SEL 6.3. A 6.3 liter overhead cam V8 sedan that got into the 14s. Since Ford never put their overhead cam V8 in a '60s Mustang available in showrooms, I will let Mercedes in. This car is the reason Mercedes use the "6.3" badge on their cars today.