I disconnected the battery while welding them in, so it self tuned to that . There is a subtle change in the exhaust sound. It sounds smoother and is ever so slightly quieter. I think it might have lost a touch of top end, but it might not have. It's too hard to tell without time slips. It did add a little on the bottom end and the car runs ever so slightly better/smoother off idle. I think it likes the back pressure.
They absolutely cleaned up all the hydrocarbon smell though, and with such limited effect on performance, I recommend this change to others who are looking to clean up the noxious odors of hydrocarbons on their street rides.
My air cleaner is still too restrictive, and I am trying to figure out what will fit on there and feed cold air to it throu the cowl. I will probably gain more from that than I might have lost from adding cats.