Keep in mind that these cars were mass produced, and have several rubber parts supporting various components so the exact dimensions of those "tight" spots vary from car to car. I'm sure that every header manufacturer strives to create a product that fits the application, it's hard to do when the dimensions vary! That being said, the "best" fitment I've experienced was Shoenfeld. I'm running large tube stepped primary pipe and 3.5" collectors, and the only slight interference I experienced was the mount for the slave cylinder (third gen F-body 5-speed). The only drawback with Shoenfeld is that they're race car stuff, so they don't have street hookups and I don't think they're available in coated, although that's easy enough to have done. Several people on the Yahoo G-body group recommend them as a best fit for the chassis. Just my 2 cents worth.