As with an intake or cam change, it may be helpful to recalibrate/optimize the carb (jets/squirter/accelerator pump) to get the most out of a change in the exhaust system.
I agree! The articles I posted were just bolt on and run. They show a positive trend for headers. If the engine was tuned after every change the trend would of been wider IMO.
I recently changed from 73 340 exhaust manifolds to Summit headers and their 2.5 inch exhaust and the performance is night and day.