Heavyweight modular book holder

I wanted a heavy duty, robust solution to hold up big art books and couldn't find a good solution so made my own.  This is a modular system so each piece can be removed or adjusted.  The pieces are:
 

1. a large, center holder section that can be freestanding by itself.  If you wanted, you could print only build plate #1 and be in business holding large books with just this
2. removable, reversible page holders.  You can forgo these completely if you want, or you can use them in the short or tall positions, or in the near and far slots depending on your book.  I advise removing them when you are actively flipping lots of pages, then insert them when you are reading or studying a painting or whatnot
3. a long “backbone” piece that the other holders slot into if you are using the final pieces below (#4)
4. The two end pieces which support the largest, heaviest books with thick covers.  You can put these on the ends or you could put these two in the center.  If you print both build plates, effectively you have a modular system that can make 1 super heavy book holder or two medium sized book holders by slotting these end pieces into the center.