I just ordered one. The last couple times I've driven home from the lake I've had a bad headache. I know it's from wakesurfing and sitting in the back corner of the boat. Not so worried about myself as all the others that are now hooked and want to go wakesurfing with me. I got on Fresh Air Exhaust website, found their number and called them. Spoke to the owner at length...they are the same people that make TrickBoardz...so I know they have a vested interest in making the sport safer. He explained all of the measurements he needed and asked if I had a plate. I don't on my boat, but he said they make them all the time for boats that do. On their website they show how to measure and one of the photos shows measuring for a plate. Here's their info.
http://www.boatpipes.com/Installation.jsp http://www.boatpipes.com/Measurements.jsp http://www.freshairexhaust.com/ Fresh Air Exhaust 512-647-7321