Header fitment problems are many times connected to the motor mount issues. The safest bet is to stick with OEM motor mounts. Personally, I prefer the aftermarket types, like Energy Suspension or ProThane, etc. The problem is that some of the after market motor mounts lower the engine, some up to 3/4 of an inch. Remember, the headers bolt to the engine so when you lower it in the chassis, you are lowering the headers, too. Headers for production cars are orginally designed to clear things under the hood like steering shafts and chassis parts. And many times, even the sales people that sell aftermarket mounts do not realize that they may lower the engine. But here is the good news, there is an easy fix. First, undo the bolts (two per side) that attach the engine mounts to the engine (even with the bolts out, the engine will still remain in place). Second, with a floor jack under the oil pan, gentally jack up the engine 1/2" to 3/4", or until the headers do not touch anything on the chassis. Use some nice flat washers between the motor mounts and the engine and stick the bolts back in and tighten them down. And now you won't need to dimple the headers...