Just went through this for my 1966 coupe 289. Purchased a single exhaust system in aluminized steel from Waldrons as they're down the road from me. My car came with a resonator - so I had Waldrons add one to the system - you can order it with or without. Will be installing it on Monday and can let you know how it fits. Quality looks very nice.
Did some research and asked around. This might not apply to the very early cars, but NPD sells the correct hangers and clamps for the 1966 model year. Waldrons might be willing to make a specific hanger, if you can't find one. So far, I've been impressed with the customer service from Waldrons.