I’ve got Borla ProXS mufflers, 3” exhaust with X pipe all the way out the back on my 68 Camaro and I’ve been very pleased with them. They have a great tone, are pretty mild overall but just like any exhaust, depending on the speed and gear selection (6 speed) you can get get some drone going on but a 2-300 rpm change in either direction cures it. I plan on using these mufflers on my 67 Nova project as well. Here’s a YouTube video of my Camaro for a sound sample if it helps…