RE: Where would I put my CG?
Hay Dave;
One thing you can do if you can't find an extension for the engine is to put an extension for the motor mount such as a box extension on the firewall of the correct length to get the enging out to where you should be. As for the muffler, you can always get a custom muffler made to fit the engine, although that is a little extreem and costly, but you may be able to make one yourself. Make a strap-on type and wrap it around the back of the engine so it is not sticking out the side. Something like the Top Flight muffler that mounts to the firewall and then make an exhaust manafold with a rubber extension to go to the muffler itself. Yo may find one already made and adapt it to your engine. There are many things you can do to put a muffler on the engine.
Good luck with your rebuild. It's a fine looking plane and worth the effort to get it fixed up.
Ed