As a one design guy I rarely get involved in discussions about modifications. Unlike most PHRF specs that use multiple measurement points,
J/30 Class rules only specify a half width (5.12.2.3, aka mid girth). Numerous attempts have been made to increase roach at 3/4-7/8. You could add runners, a backstay flicker, or drop the halyard before every tack, but if not, don't be surprised if you have trouble getting the mainsail past the backstay. It will drive you crazy downwind, especially in light air.
