I bought a set for my 94 SS. The installation and fit was about equal to my experience with other manufacturers - it took a bit of farting about to get it to work. Once installed - no problems.
I did have one quality issue - the O2 sensor fitting on one of the headers was improperly machined. The guys at Moto Wheels took good care of me and swapped it out. Great service!
I didn't have cornering clearance problems before, and don't have them now. Therefore, I cannot address your clearance question. I, too, have a +1" Penske shock. I suppose I would try a higher preload if I had clearance issues. I currently run mine with a fair bit of preload. It's a bit rough on railroad crossings and potholes, but otherwise excellent.
I would buy these headers again.