Oh indeed! It can be any size, 84 seemed an easy standard to find. 7Ux126HP is a bit larger than I am ready for just yet, all that empty space will drive me nuts and lead me to want to expand too fast.
I picked 84HP to try to limit my build out of the system. I guess I'll end up with a hermit-crab like series of slightly
larger shells that way. Maybe there will be someone else out there that wants a wood 84HP box at the end of this journey... I could post pictures of the build as it goes, I have the DFAM + 60HP currently mounted with plywood sides that copy the 2-tier rack look (but in wood) and it looks and feels nice as a unified instrument.