I'm running Xr-1s with a BBC...not too loud at idle and screams when you put your foot in it.
Here's an older video with the mufflers dumped in front of the axle. I've since added tailpipes and it's a good bit quieter and higher pitched.
By the way, I'm running a Ram Air restorations oval x pipe kit from the headers to the mufflers. It's a nice kit, but the transitions from oval to round to go into the mufflers are too long (which keeps you from tucking it up much). I kinda feel like they defeat the purpose of the oval. Just my .02.
I really like the XR1's. My only complaint is I kind find them with an offset or outlet which would have helped packaging.