I wrote an openscad script to re-create the box parametrically with a variable for an interface margin. This means you can set the variable fit_margin based on measurements from the actual ribbon or play around with what works for your printer.

I also scaled this up by 889% because the model was itsy bitsy.

Play around with fit_margin if the channels are too small for the ribbon to fit into. For me, it was around 0.5mm (This accounts for 0.25mm on each side) when printing at 0.2mm layer height.

Print the ribbon with support material everywhere and don't be afraid to slow it down!