some clues (thanks to servicing masts on Maramu 1982) concerning halyard stuck inside the mast
halyards are running Inside mast independently from cables (electric, signal);
cables are run through pvc pipes (2 x dia 32 mm) held by rivets or guided on rail;
one place where halyards can get stuck is at top where cables are coming out of pvc tube;
other place is on rivet heads (or bolts if modified ?) holding mast fittings in place;
other place is rope jumped out of pulley block groove at top of mast;
one trip up the mast with Tools to remove screws holding mast fitting in place & a good look Inside mast seems to be the way before pulling rope with winch.
Wish you luck & a good trip to the top.
cheistian alby - Desirade VIII Maramu 116 now in Canet