On the R21 I recently sold, I used the lower 12' 6" of an Aluminum windsurfing mast, and ran it back to the main beam just below the mast base, secured it mid pole below the jib bridle with lashings, with wires running from the pole tip to the tangs on the bows. Worked very well for both a roller furling screacher and an assym spin. Had a ss cap fabricated for the pole tip to prevent crushing, and a socket created out of a section of alum tubing just larger than the butt end of the pole with a rectangular plate welded to it that I then secured to the main beam. I'd advise against butting the pole to the front crossbeam, the compression forces on the pole are pretty substantial, the main beam is much stouter. Feel free to call me.
Dave 509 276 6355