My 79 Corvette came with 15"x8" alloys from the factory. They were wrapped in nice 255/60/15 tires all around. This was once considered as a low profile tire! One of the biggest improvements you can do to your C3 Corvette's handling is to change the wheels and tires for bigger diameter wheel and lower profile tires.

I've never liked soft riding cars, so I went for the extreme wheels and tires combination. I'm using 20" American Racing Torque Thrust II all around. I have 20"x8" in front with 255/35/20 Pirelli PZero rubbers. In the back I'm using 20"x10" wheels with 285/30/20 Pirelli PZeros. Note that you'll need custom back spacing to accommodate the 10" at back, plus you'll need offset trailing arms.

Using low profile tires makes huge improvement to the handling or the car. It feels a lot safer to brake hard now when you don't have to worry about the old wobbly tires. Acceleration is also somewhat easier since the car tends go straight instead of pulling from side to side.