So basically after downloading the AOSP repo, I tried to merge the LG ROM and the Android Source, but after banging my head against the wall for almost 10 hours, I ended up giving up and resyncing the git. From there I merged the ROM, but this time with some more experience and I think it has worked; the ROM is compiling as I type this.
Here are my findings:
1. It appears LG includes an 'external' directory. This directory appears to have some necessary libraries, but in reality it's missing a lot of stuff. Before I tried overwriting the 'external' directory in the AOSP directory, but it wasn't working, so this time around I completely ignored it. tl;dr leave the 'external' directory as it came. LG's version appears to be deprecated.
2. In LG's included 'frameworks' folder, there is a test-runner.zip. I extracted that and replaced the test-runner inside my AOSP/frameworks/base/ Maybe this will solve it?
3. I moved LG's 'vendor' directory over. Not much in there other than some stock apps.
Like I said earlier, these are just observations and not fully tested. The ROM is still compiling, and even if it does compile, I'm not sure it will work. Take my advice only with a grain of salt, and please don't hate me if something doesn't work
Maybe @azvampyre can chime in and give some better advice? Or put up a tutorial? If @azvampyre reads this, I can help run other compiling because I am on a non-VM Linux machine, so it might improve the build time/success rate.