Yes, GMC starts at Cutty Sark Gardens by the Gypsy Moth Pub. I'm doing a final route check this weekend and will send out the routesheet/GPX in about a week's time. Note that the return route is through Bromley, Grove Park, Lee & Blackheath so you could probably just use that to get to the start, though the Arrivée is at my house, so don't end up there, but carry on down Crooms Hill after the Tea Hut.