I had the same concern about the Borgeson shaft. The Flaming River shafts use the same setup. My solution was to drill point the shaft. I also used square head set screws. I crossdrilled the heads and then saftey wired them with aircrafft saftey wire.
83 CJ-7, AMC 360, RV CAM, GM FI, AUTO WITH SHIFT KIT, FRONT DANA 44 HP LOCKRIGHT HIGH STEER, REAR CURRIE 9" HP SHAVED AND SPOOLED, 37" PJ DIRT GRIPS, AJ'S BODY FENDERS AND HOOD, WARN HS9500, OBA, BESTOP TOP AND SEATS AND STILL GOING.