As to timing, I usually recommend 6° btdc as a good place to start; however, that can vary depending on altitude: higher altitude needs more timing, something like 1-2°/4000' ish. I'd call it a "feel" setting, which is to say, give it to her till she feels good. You can apply the same technique at sea level and be fine but, again there are variants at work that need to be considered such as fuel quality and the load that'll be put on the engine during operation. For example, my 345/DUI runs like a top on regular gas around town and on the highway at 12° btdc, it runs better at 15° btdc, but if i try pushing it up over grapevine or cajon at 15° on regular gas itll ping where with premium, it won't. Higher octane fuel burns slower; more complete burn equals more energy, probably better milage to.
Having ssid all that, my "opinion" on how to set the timing for your 345/pertronix is to start at 6°. Then set it at 35° "all in". Itll take 36, but no need to push it that far. Whatever that comes back to at idle, is what it is. If you want to back it down a degree or two from there, that's fine. The other way is to just give as much as itll take under heavy load until it doesn't ping. That's kinda what your after anyway, no ping, running balls out. Just keep in mind its a Scout, not a street racer.