Measure, then shop.
Fred, to repeat, you really need exact dimensions. Measure your current sail and don't worry about I and J. Then go to the used sail websites, I'll put a couple of addresses below. But I still think you need to involve a loft. Not only are there three dimensions(luff, leech, and foot) but also the weight and material of the cloth. And there is the luff tape size, it has to fit the groove of your furler. I paid less than $1100. for a new jib(H37C) from Lee(Link below), a much better deal than chancing a good used sail for $700. Other links: http://www.baconsails.com/(check topic "measuring" for I