Advance Design steering shafts are solid steel, not hollow...about 3/4" or 13/16" dia. The horn wire is run inside the mast jacket. Sectioning/shortening steering shafts is pretty common place in the street rod world, and as Stuart stated, easy and safe if prepared properly and done by a skilled welder. Borgeson Universal Joint Co. sells weld on couplers/adapters for smooth shafts. They can also be pinned.
#4 still may be the most rewarding...
