Gunner, I have owned a few British bikes, and my experience with them might help you out. My first was a BSA 650 with all the positive ground British wiring, and although the engine and chassis were in great shape and I loved the sound of the bike, I fought with its wiring from day one. I knew nothing of electrics, and all of the other British particularities (such as Whitworth bolts) p***ed me off to no end. As much as I liked that bike, I ended up trading it away.
About five years later I acquired a Triumph Bonneville 750 as part of an
automotive engine trade. This bike was newly rebuilt and ran well, but I was having the same electrical problems that I did with the BSA. But this time I bought a few books on motorcycle electrics and learned what I needed to know. With no experience other than wiring a few car stereos, I yanked the Lucas system out of the bike, trashed it, and developed and installed a new negative-ground system. It can be done!
It started as a basic system with CDI ignition in which none of the lights would function unless the engine was running. But I later added a battery and regulator to the system, which cured the wiring problem. One important factor I learned was to always solder your electrical connections (after crimping) to counter the vibration of the bike. After I replaced the Amal carburetors on it with Del Orto carbs (I must have been trying to Harley-ize the bike), that joker ran like the wind, and handled even better.
But I could never stop that leak from the primary chain adjuster. I wish I could go back knowing what I know now.
Because you are planning to convert your Constellation to a rat bike, you might consider what I did to that Triumph. It was not really that tough to do, and everything performed well after my wiring changes. And because I did the work myself, I understood it much better. Sounds to me like that would be a good way to go with your Constellation/Meteor.