Nice! Personally liked seeing how Aluma Core V1 is/was taking shape, and evolving.
Still open to rotating X axis 90 degrees, would that help a plate(s) based Aluma Core design any?
Maybe flanged linear rails block with rear access holes, or, two plates that fasten together.
Two plate approach could maybe also help fasten/hold the belts too? Otherwise additional smaller 3rd/4th plate(s) needed?