You want to be able to get 110 degrees of rotation downwind.
This is what I did:
I bought a mast rotator arm for a boomless from Murray's that is Like a V going out from the mast and straight across the back. I use the system for a Hobie 20 with two snaps rings, three pieces of line and shock cord. Tie the line across the bridle connectors at front of beams. Then with line tied to holes in mast rotator I clip one end of shock cord to rings and loop it around front line and back to rings. This pulls mast forward for downwind to 110 degrees. For mast rotation I have a small pulley system with cleat that attaches one end to boom and other to mast rotator. This sets mast rotation. Hope this make sense? If not call me.