I’ve printed up pieces uploaded this morning to Thingiverse, tried them together, broke two pieces, modified them, printed, and fit some together. I’ve just modified the STL for what I hope is the last time. However, I have the barbell fit snugly into the center cube. It rotates relatively freely and does not want to pop out. (Of course, I’m sure it could/would if I applied enough force). This leaves the outside cubes. I modified the semicircular tabs a little and will reprint them later.
The only problem is that it takes about 40 minutes for my machine to print up two cube parts and a barbell, since they’re so solid.
The important thing is that I’ve just been able to print up and assemble the crucial mechanisms for this puzzle. I think the next iteration may be what I needed.