FYI, the correct spare wheel for your car is a 15" x 8" steel wheel (rally) with 4" of backspace, coded AZ to the left of the valve stem (1969-82 Corvette). Aside from purists wanting the correct wheel, the coding is important to ensure that you get the correct wheel backspacing, in case you ever have to mount the spare on the car. The AZ wheels will work as a spare up until the 1978 models. The '78-'82 Corvettes take a compact spare tire. This is due to the increase in fuel tank size compared to the earlier C3s.
1968 Corvettes were 7" wide.
1967 Corvettes, the first year for rally wheels, were 6" wide.