@burvantill
First, very cool looking book idea!
I'm always intrigued by questions like this!
What you are suggesting seems to me to be less of a copyright infringement and more of a trademark infringement.
So while my opinion is that this is a "technical" infringement, you need to answer whether this is an "actionable" infringement.
The answer to that may be clearly spelled out by Lego itself! I did a search and came across this youtube video:
https://youtu.be/7CQZRtTtUSA
which led me to this PDF from the Lego company:
https://www.lego.com/en-us/legal/legal-notice/fair-play
which instructs those who wish to make books using lego brick to contact Lego for more guidance (this is also mentioned in the video. Apparently the Lego PDF guide on what is allowed for books is something they don't publish online. You have to request it)
So it seems that Lego is more flexible than most about how their IP is used. I would love to know what you find out!