A way to mount motors in a tight space is to mount them back to back on a vertical ply plate using a couple of Terry Tool clips. They come in a wide range of sizes and two per motor should be enough. Strong,firm and makes for easy removal if needed. Here is a link. Or Google TERRY TOOL CLIPS.
https://www.google.co.uk/search?q=terry+tool+clips&oq=Terry+tool&aqs=chrome.1.69i57j0l5.14582j0j7&sourceid=chrome&ie=UTF-8👍
Clips best fixed to the plate before gluing it in place if using screws although they could be epoxied in place with the plate in place.👍👍