I got a response from TwistedThrottle.com. They said that the Givi A620 fork mount is too narrow for the 55mm diameter TBA/SM fork covers...buggernutz !! Too bad, because I had just figured out that the screen would not obscure the handlebar mounted front signal lights, and that the fork mounts could be move down the forks enough so that they would not touch the fuel tank.

'06 Speedmaster, Long TORS, rest is stock (for now)