I've got a pair of Flowmaster 50s under my '62 NewYorker wagon.
It has a stock diameter exhaust and the engine has carboned-up the mufflers pretty good to have given them a fairly toned down sound.
I kinda like it because when the engine is idling or when driving you can hardly hear there are Flowmasters under the car. It only is noticable when getting on the throttle.