Nice build.
Here are some of my thoughts that may or may not prove to be helpful for you.
1) Copper oil and gas lines. Do it. I am on my build. I wanted to keep this as my little secret until I got to that point in the build. I think it's the little details like this, that are steampunk and still functional (as opposed to just for aesthetics), that will just kill. Try and get a petcock that uses a compression fitting instead of the standard barb. If you use an oil pump with external lines, use it for your external lines too.
2) Copper braided brake hose. Copper doesn't like brake fluid (ok with oil and gas), so make sure it' just on the outside.
3) Cut away material on your sprocket cover so you can see the sprocket turning. I'm drilling holes in mine. You could just cut a "window" or some sort of big hole, or cut out a pattern or design.
4) Anodized chain and sprockets. I'm not sure if copper is available, but gold should be easy enough.
5) If you have the funds, get a dry clutch. It's exposed, and sounds great too.
6) Get one of those old style megaphone horns.
7) Get a hand pump for your fuel tank.
Take a look at this:
http://www.revatu.nl/peashooter.php
edit: typo