Pine should work well. Check the grain to make sure it is nearly parallel to the board. There isn't really a tight bend to the gunwales so there's not much strain on the wood.You're lumber supplier may have tighter bends in mind. Red cedar, aside from being expensive, is very soft (mortices loosen quickly) and short grained (prone to fractures). Ash is indeed heavy for use as gunwales. It steam-bends well so it will work for ribs, especially if you're able to get it green.
I was at Home Depot this week sorting through 3/4" pine boards. I always start looking at the widest stuff (12" and 10")because there are more clear runs to be found there than in the narrower stock. I found a few 1x10s that were nearly clear and had fairly straight grain.