So choking down the exhaust flow coming out of the RN waterbox creating more back pressure.
I'm using a SN Factory Pipe Waterbox. I already had the 2" SN exhaust hose, 2" SN elbow from the B Pipe, a Factory Pipe 2" SN waterbox and all of these pieces are going into my RN hull with the stock 2-3/8" RN rear aluminum exhaust tube going out the rear of the hull.
Could you use a long rubber SN exhaust tube on a RN hull and 2-3/8" exhaust components, yes, but I wouldn't do it, because like Big Kahuna said it would choke down the exhaust creating a bottleneck since everything being 2-3/8" and then going down to 2" and back to 2-3/8". If I had a RN waterbox and RN B pipe exhaust elbow I would have got the correct RN long rubber exhaust hose too because I wouldn't have wanted to choke the exhaust down.
The SN parts that I had all worked great together when they were in the SN, so I just basically swapped all of them into my RN fixed steer that I'm building. Everything that I described in my previous post was about taking SN exhaust parts and fitting them onto the 2-3/8" rear RN exhaust tube. So if you have a SN and want to take the exhaust components out and put them into a RN hull, it'll work since everything from a SN is 2" and it'll exit into the 2-3/8" rear RN exhaust tube out the back of the hull.