early a engine swap

The Durango or any other late model manifolds will absolutely not fit in an early-A with power steering, regardless of how much grinding you do.

I know this from direct experience because I've tried a number of exhaust options with the 360 in my '65 Barracuda. The only realistic exhaust options for a V8 with power steering are either stock 273 manifolds (which I believe will work just fine for a typical 318 ) which slip right in with a minimum of fuss, or you can go nuts with Doug's or TTI headers. That's it. I currently have Doug's in my Barracuda but I had to tear out the steering, brake lines, z-bar, starter, wiring, etc., to install them and then fabricate new brake lines, fab up a hydraulic clutch system, modify an expensive steering coupler, weld up a special bracket for the brake booster, and purchase a very expensive clockable RobbMC starter. It's a spectacular exercise in spending money and shop work.

Unless you plan to hop up your 318 to high output, seriously don't bother with the headers and buy a pair of good, solid 273 manifolds. Go dual exhaust if you like for the sound, port and polish the exhaust joints to match if you have the time and inclination, and enjoy your power steering.

PS: In many ways I wish I had a hopped up /6 instead of the fat 360 I have now. If I ever buy another early-A, I would build up a /6 turbo and enjoy the benefits. You might dig around a little more to find a good /6 motor before you go for a V8 and then find yourself re-engineering the rest of the car to suit. You'll be bucks ahead, but this is just my opinion.

-marcus