Here are photos of my 3" undercar exhaust. The mufflers are low restriction from SpinTech that they made to fit the area I had available - don't know if they still do that or not...
The upcharge for the mufflers was quite reasonable. Of course, that was nearly 20 years ago!
It's fairly loud even with the big mufflers. I had to reduce the width from the first set as I didn't quite allow enough space between the mufflers and the outriggers and chassis. The engine moves a bit more than I allowed for at first. Second set is still on the car.
No problems with ground clearance so far.
The last shot shows the car from the outside so you can see where the exhaust ended up.