69 Tires

A 70 series tire is what the '69 body contours are designed for. Whether a 215 or 225 fits is an individual car thing, as already stated. The 215 is closer to an F70-15 dimensionally, but many cars can take a 225 without problems.

The 215 will give a more accurate speedometer reading, the 225 (assuming there are no fit problems) will give better tire mileage and gas economy, at a slight cost in acceleration, which may not even be noticeable.

While you can likely get better handling out of a 60 series tire, you'll probably get a worse ride. The wider tires tend to find every little stone and imperfection in the road more than a 70 series. When Chevrolet started making 60 series tires optional with the '78 model year, some early magazine test reviews reported as much.

You pays yer money and takes yer chances...