Good plan Tim,
Getting on the road late October is a good plan, Baja will still be a bit warm but by November things cool and your ride through the rest of Mexico and through Cent. America should have best weather of the year. Rainy season over, cooler temps. Once onto Colombia seasons sort of reverse, harder to predict weather.

If you don't hook up with any co-riders before departure I would go anyway. You'll run into lots of riders along the road. All through Baja, parts of Mexico and Cent. America. Oct. to March is popular time to ride so quite a few riders will be on the roads during those months. Research Research Research!

There is some support and knowledge down South for old Air Heads, especially in Guatemala in the XPat community there. Seems like the elec. and charging systems on those old bikes are suspect, so pack spares as needed and start with a NEW battery and ALL GOOD components.

Same with final drive. Perhaps do a total rebuild of driveline before departure? or pack a few key bearings and such. Take care the fuel system too, fuel filters good, keep carbs clean! Many BMW riders break luggage racks if going off road. But good welders abound ... so no real worries there.

Make certain you shock is fresh, hard to find suspension guys ... but there ARE some around. Best refresh shock, fork seals.

All the best with the planning!