Biggest hurdles...finding a 6v signal kit & figuring out the actual signal stalk assemblies to use + where/how to mount them.
No need to replace your existing harness. You can "T" into the horn/brake light circuit, voila! switched power. I'd just run the new add-on signal wiring with the original harness. The exposed ends should fit through the sheathing, electrical tape can handle the rest.
There's not much untapped "reserve" capacity in pre-signal era models. Thus, it'd be a good idea to upsize the battery and source an LED signal kit, with an electronic flasher relay. Just sourcing a sealed, 6v AGM battery will give you roughly double the charge capacity...in the same sized unit. The K0 battery carrier is a lot larger than K1, so it may be possible to fit a larger battery, or possibly a pair of AGM type (wired in parallel), by replacing the thick rubber spacers...if you're looking for some overkill.
As for the stalk assemblies, themselves, I'd replace the tail light assembly. The Dax version bracket retains the K0 light asm and adds signal mounts to either side of the license plate. An integrated tail/brake light & signal unit could be sourced, from another model; you'd need to fab your own mounting bracketry. Up front is more difficult. I'd want to avoid mounting anything to the headlight ears...too damage-prone. That basically leaves the handlebars themselves. Rubber/polymer stalks will give you some added damage resistance and are fairly common among aftermarket kits.