Jerry, you are right that it would not be normal for the full output of the alternator to go to the battery. I don't think I implied that it would. But regardless, to protect the existing wiring harness against unintentional shorts or higher loads, the as-is wire should be protected based on its gauge - 10 AWG typically protected by #14 fusible link, and typically 3-4" in length.
Perhaps my suggestion about considering a change to 8 AWG was confusing? What I was thinking about (and didn't articulate - fair enough) was that add-ons can quickly increase the load, and since the alternator can provide more than 55 amps comfortably, an upgrade to 8AWG would allow the system to take full advantage of that (for lights, sound, whatever), with decreased voltage drop, whether the current comes from the alternator or battery for those accessories. It was intended to be something to think about - not a go-do - which is why I stated "consider."
BTW, this is my field of professional expertise. I'm not a machinist, nor have I had decades wrenching professionally, but I have worked in a shop - engine work in particular - working evenings and nights back in the '80's to early '90's. My first tear down of a 235 was in the late '60's. Electrical systems are another matter. I made a 40-year career out of this area, starting as a tech while going to grad school. Many years later, I used to lecture the engineers who worked on my projects: "get off the carpets and down to the linoleum [factory floor]." I heartily agree that practical experience is priceless.
