Is this VIN a 68 340S?

Correct, tachs were an option, the "performance indicator" was also optional... my '68 didn't come with eather. My car also came with an open 3.23:1 8 3/4, 4 wheel HD (10X2") manual drum brakes, and white wall tires, dlx. hub caps, and the 14X5.5 wheels.