Remove volume and tempo knobs:
By removing the existing volume and tempo knobs you can gain some valuable space on the front panel for the rest of the knobs you need to add. I replaced them with Jaycar's 9mm pots in identical values and a seperate toggle switch for on/off (see pictures). When doing this you can remove the metal supports for the removed knobs but they are used as conductors so you'll need to install some wire links.

Front panel:
After removing the unnecessarily large knobs there is heaps of room for new controls. To fit the pots inside the case you'll need to create a new face plate (it gains you around 2mm) and mount the knobs to this. Be careful where you choose to place the pots on this new panel as you need to cutout a window in the old face to accecpt the new pots and there are several standoffs that need to keep in place to hold the case together.

I have used a slighly non-standard designation system on the schematics. New parts have an X sufix to the designation and all other items are referenced to the orginal schematics. Any parts that need to be removed are noted in the text.