I figure you've probably already resolved this, but for anyone else who runs across it, here was the solution:
Essentially, you just have to close all of your editor windows in Visual Studio. A close & restart of Visual Studio won't even fix it.
Coincidentally, Bryan, I think we probably have very similar Kentico configurations because we have run across the same issues that you posted in a different post about having to create a "finisher" deploy for each upgrade version. So far, we're having problems with 8.2 even with a "finisher".
We also encountered the issues with System.Net.Http. We will try your solution because 188.8.131.52 doesn't seem to build properly.