Get creative and build a mount for the second compressor. Or buy an electric compressor for OBA. So many technically correct options and here you are talking yourself into a total embarrassment of a hack. Those guys up there responded tongue in cheek - you missed that. It is a total mistake and hack to use a window unit. One of many reasons that is not a good idea is that they are not designed to handle vibration. But so what? Go for it, pardner.
If you persist, post a build thread and update with real-world performance as we can use the laugh.
Dual compressor mounts were pretty common for the Jeep series for just this reason. I'd really look into that vs the discussed alternative.