I am not a believer in the use of headers (unless you're running a highly modified, high horsepower engine) due to cost, maintenance, and lack of added performance benefit in a basically stock engine.
An engine is basically an air pump. It sucks, squeezes, burns, and blows. A stock 289/302 nominally draws in 500cfm thru the carburetor. (Larger carbs are of no value, as the valve chambers can only handle so much air.) Consequently larger exhaust pipes are of no significant benefit. Lower exhaust back pressure is of minimal benefit, if any. So, unless you're building a powerhouse engine (ala Rob):grin: the cost outweighs the benefits. Just MHO.
Neil