FuryFan, I made the set on my 69 Cuda and they are quieter than stock when closed and as loud as Flowmasters when open. They have zero resonation when closed and they roar when open. They flow like stockers when closed and even though this is not anything to brag about, they pass as much air when open as the equivalent sized Flowmaster.
They are expensive but offer a person the way to have the best of both worlds. For sure, they are not drag racing mufflers, they were not meant to be. I did a lot of tricks inside of mine to bump the air flow up and the ones that Waldron sells are darn near as good, air-flow wise.
For our A- cars, the 18" cases will fit fine although you need to drop the nose down a tad to clear the 4" actuator needed. For Bs, you could use the 19" or 20" case size.
The sound levels depend upon engine of course but I saw around 9 to 10 dBa difference in many rpm levels on mine.
The first video is a true 1970 400 VOE GTO. The second is my car with the stocker VOE mufflers. Mine are louder than the VOE GTO versions. The set below in the photo is on a 1969 Cobra Jet 428 Torino.
http://www.youtube.com/watch?v=Mwov5Kp0SCEhttp://www.youtube.com/watch?v=oX5i4_CQqb8&feature=relatedTom Hand
