You don't say what radio and whether transmitting or just receive.

Certainly you can use the shrouds, but not advisable for transmitting, all of the metal bits of the rigging would be live with RF which is not recommended.

Should make a decent receive aerial, but will be best if you connect well up the back stay or shroud rather than the bottom of the wire.

Dunno what a "chocolate block" is but I would use a couple of Jubulee type clips, solder the end of the wire and connect it with the end of the wire pointing downwards. A spot of waterproof sealer will complete the fitting.