BTW - would be great to see some photos and rough measurements of one of these J/30 gin poles. I've used one on a J/24 many times - it was basically just an old mast segment. At the base, it had a block of wood that was cut so it wouldnt slide around.
It then had 3 "guy wires" running from the top that were attached at 3 points on deck and made very tight.
At the top it had a small block which i think had like a 4:1 purchase. You would tie the end of the line to the base of the mast, and a loop around mid-way up to keep it lifting straight.
SO you basically had a personal crane.