Doug's Headers in 64-66 A-Body
I was just working on my 66 this weekend. They fit like a glove on my 360 w/ power steering, power brakes, 10.5 clutch.
Couple of note able items. You can use a standard late model 5.9 starter rather than a high dollar exotic. On the passenger side the header tubes come pretty close to the fuel and brake lines. I re-routed my brake line on that side and m going to put some heat shielding on the fuel line to keep the fuel temp down.