Just a small update for now:
The first step in working with the current engine was of course to make sure the current code was functional. However upon integrating the Joefish Immortal branch into my fork, I found that the code had several compilation errors seemingly connected to the metaengine system. Luckily, there was very recently a new tool added to ScummVM called create_engine. This development program automates much of the engine skeleton creation process, and does so with up to date ScummVM conventions. So to make for a cleaner start (at the suggestion of DreamMaster), I used the create_engine tool to replace the current engine skeleton with something more up to date. This allowed me to then add back in the Joefish code, and after a little fiddling, get it to compile. Now the current code is able to run and I can move forward with that.
Once the code compiled and ran, I needed to update my remote repository with the working code. This proved to be much more time consuming than I had expected, as I found that I am still having trouble getting used to how Git works and how to use it effectively. I ended up unintentionally adding an extra version of the Immortal directory in both the master and the immortal specific branch, and in the process of trying to fix that caused more issues with the local repository. Thanks to Sev and Criezy I was able to fix these issues and properly update my remote repository with the working code. This process showed me that I need more practice using Git, and I will hopefully now have fewer of these issues in the future.