If these are ribs that going to be tacked into the stems, they're more like spacers than anything else. I'd be tempted to cut a kerf in them where they hit the stem, to ease the bend.
All you want there is a neat fit. That rib is there to nail planks into, not add strength. As Rollin said in another post that kind of rib could just as easily be a cant rib. So long as the long gentle curve of rib is good enuf, you are home free.
fitting it around the stem can be tough. Alot of planking would have to be removed to get it to go in. that's why those ribs get backside repairs or are put in like cants.