The tuned pipe can be difficult to find. The most popular ones is the Texan .12 Pipe. Or the Carbon Fiber Raptor .12 Pipe. They were handmade by a few fellow rc boat racers, but they are no longer building them. Another option is a Macs .12 Tuned Pipe Part #1110. Unfortunately the owner passed several years ago, so Macs Tuned Pipes is no longer in business. I would post in the for sale section that you are trying to find/buy a .12 pipe, Definitely worth a shot. I have seen pics of .12 Riggers with nitro rc touring car pipes, but I’ve never tried one on my 12 rigger, so I can’t say how well they may work in a boat. The header is available from Novarossi Marine USA. they sell a wrap-around 180 degree header for .12 engines on their website. If you do a search on this site for .12 riggers or .12 Novas, you should find a tons of info on JAE 12’s with .12 Novas and pics of those tuned pipes.
Brian