Looks great, I am just scared for your servers falling... may I recommend these: 2U angle bracket My office has used something similar. I have a few in the basement on the ceiling.
A pair of these front and rear would make wall mounting the R720xd simple. By using a pair instead of just one you can maintain proper airflow by keeping it horizontal instead of having to mount it vertically.
Like others have said a wall cabinet for something that heavy is not recommended. That said, you can use something like this to wall mount the server. https://www.amazon.com/dp/B00ZY7AK72