Here's the side exhaust header that I've used:
http://www3.towerhobbies.com/cgi-bin...&I=LXJM08&P=RF . Note that the flange has to be opened up to match the gasket. I just used a stack of about 3 or 4 Dremel cut-off wheels, the cheap ones, to open it up as you want to angle it towards the header's pipe. Use the gasket as a template and use a Sharpie or something to mark what needs to go.
Here's one video that Mark "ob nut" Scott shot of my son driving it a few years back:
http://www.rcflix.com/photopost/data/500/612fr20.mpg
If you need any more help with the build, I'm subscribed to this thread.
Just so you know, I didn't build the hull, Mike "Grim Racer" Zaborowski did back when he had his own company. He also had some laid up in epoxy-glas.
You can do the 2 bulkheads in thick balsa if you want to but the transom has to be lite ply. Use model aircraft grade ply, not anything from a home improvement store.