Positive earth is a pain. Just about any bit you add to a car is or expects negative earth.
I'd convert like a shot, one bit of originality that makes no sense and cannot be seen either as without a voltmeter, you'd never know.
Interestingly to note, all Morgans until the early 30s were negative earth. Then the fad for positive earth came in on most if not all manufacturers, Morgans included. I don't know if it is true, but my father said it was an anti-corrosion measure, although since it didn't work, and negative earth is much more convenient, manufacturers eventually reverted.
