Rather than dive straight into modding my beloved C64 directly, I decided to make break out boxes for Analog Pots, Audio In/Out, Video Out and Feedback, to help fine tune designs.
Finished Analog Pot Box
Analog Pot Box and Feedback, Audio In/out, Video Out box
For the feedback mod I used AlphA's amazing website
and for the external pot box I used InactiveX's schematics here...