There are guides that show you how to use the whole nightstand as an 8U rack, I essentially just did it the hard way.
I differed slightly in that I mounted the 6U rack rails on top, but I also mounted 2U rails separately in the middle. Sources for this post include Kenneth Ballard’s write up, as well as this Instructables post, and this post. I found most other guides to be lacking in pointing this out, and I actually bought the wrong screws at first.
This is because the thickness of the wood is only 3/4″ inch. I would like to point out, because it is not stated clearly (or at all) in other posts: To mount the rails to the Nightstand, you will need to use 1/2″ wood screws. After following thinking it over for many months, and reading multiple guides on how to do this, I have finally motivated myself to create some studio rack furniture using the Ikea Rast nightstand.