Spot on, you are going to have to pull the trackpad from the 12". These can be tricky - sometimes they bend irreparably when you remove them. Other times they are fine.
Keyboard will be different as well so you might want to import that from the 12". You might be able to swap some of the keys over if you wanted to.

I can see the video cable being a bit of an issue too. Apple used to have a tendency to wrap them around the hinges a bit more than they do these days.