I didn't realize there was an NA mast, I always thought it was afterthought because they were breaking too many of the original single wire mast.

In looking over DP-N the only mast modification I can see is for "MT = For taller mast than standard" which I don't think is your case.

But, do you have a square top, bridal foil, etc.....? If so then even I may be a little inclined to rate you at 63.9

In answer to your question about a low wind monster they way I read the rules is they take each modification separately, and I don't see a correcting factor for carrying a smaller jib. In light winds you may want to go back to the old style.