Zoomed in on the cartridges. The Music Module is too wide for the casing so it had to be put outside of the slot expander. On the bottom plate of the casing a piece of 90 degrees bent aluminum profile was mounted so the cartridge can not slide inwards. On top the cartridge is screwed onto a aluminum bar which is put there only for this reason.
A slot extension cable connects the cartridge to slot 1.1, the second cartridge from the left inside the slot expander.