Dougs headers
I run TTIs so I can't really help much. I run the small filter without any problems. My Dodge ram truck runs the same filter from the factory.
Dougs look just like TTIs around the spark plug area so I would say No problems there. I can have the plugs out in less than five minutes.
Capture the oil pan? I have removed my oil pan before without removing the headers. I had to losing the headers up to remove the oil pan without getting very angry! LOL