No hassle headers for 66 dart w/360?

Reading through all of the posts on headers in a 66 Dart is discouraging and convincing me that the best option is keeping the 273 exhaust manifolds. I am not willing to give up PS so the rare 340HP manifolds won't work. Not cutting up the fenders. But have a 340 and 360 in the garage waiting to get rebuilt and dropped in.
Has anyone used that setup? Wondering how much the turbulence from smaller exhaust ports would affect performance.