Race Headers on a street car.

I'm still in the planning phase of a 360 based 426 stroker with W2 iron heads/ 4 speed in a 69 dart. Its not a number matching setup so.... So i i guess i need W2 headers. I see TTi and headman and hooker and others. Some have a tube that goes thru the fender well. Most race headers are 1-7/8" or 2". I was just inquiring about the difference.