The “K” represented the engine code on the VIN number of these Mustangs. The K-Code engine was first introduced by Ford in 1963, and was featured in cars such as the Fairlane and the Comet. Each K-Code Mustang had a special badge on their front fenders that read “HIGH PERFORMANCE 289”.eople often ask how the K-Code engine was different from the other D,C, and A code 289 engines featured in 1965-1967 Mustangs. Well, once again, think performance. For starters this engine featured upgraded pistons, cylinder heads, carburetor, lifter heads, and connecting rods.