Finally got around to converting this for my friend. It was pretty straightforward, and I ended up replacing every wire and jack. The wires were so skinny that they kept breaking on me and several were broken before I even got started – it was the main reason he wanted me to look at it to at...
Here’s an example of one I did a while back. I added an fx loop, but you basically use the J.Out and/or J.In wires and connect whichever one to the OJ or IJ PPCB board (or footswitch IN or OUT) depending on the order of the two circuits.