It is ATX.Very nice work man, I just noticed that you started this in 2018! Talk about sticking to your guns, most would have lost interest or motivation.
This thread actually made me get into 3d printing!
Yep, I had to use a STL for my BMG before I found the step file, my memory usage hit nearly 32gb (my max) because of it.
Also being very lazy here, was this an ATX mobo?
Thanks for sharing.