R42 is the jumper. I meant to add a note about that so I will go back and edit the doc. I also forgot to add a link I wanted in there (got pretty worn out by the time I got to the Current Lover). Anyway, some versions of the Mistress have a 10k in that spot and some don't. The link is to documentation showing all the differences in the classic versions of the Mistress.
For the loop, I only ever saw one or two people do it so I left it off. You could certainly put one in there. I think maybe doing as single TRS Marshall style jack might still fit in a 1590BB.