I have done this. The net cost was basically zero as I sold the furling unit on eBay for more than the cost of a minor sail recut (adding a triangle at the bottom to get the foot sweeping the deck), getting the battens switched to horizontal, adding hanks and swapping out the forestay (which you should do every 10 years anyway).How easy is it to change a furler to a head stay? Just get a rigger to do up a new head stay? Can i change the existing furled job quiver into hanked horizontal battened sails? Or am I buying new jibs?
You only get IRC furling credit for overlappers >=130% of J. Not relevant for the standard 105 jib IIRC.A furling sail will always be less efficient than a proper jib with horizontal battens. If you are racing in IRC your rating will probably go up slightly but for me it was worth doing.