Unless you have been inside one before, I'd take it to a smith. I'm not saying you or anyone else can't work on the HRs, because they're simple for the most part. It would e best to get someone professional to mess with something safety related such as that, because you'll probably feel mor confident about that in the end. The entire trigger/hammer group has about five or six parts in it, including the hammer and trigger guard, so you could just get the other few parts and take them to the smith and let him show you how to install the stuff, if you wanted.
Here's a thought: Let the ducks work and decoy.