If I was at home right now, I could easily answer your questions, but I'm at work and won't be home until Wednesday. I've built two of these, and have a third kit at home now. I think if you read the directions/manual closely while looking at the plans, the pieces you're asking about should be identified. If memory serves me right though, everything in the area of the cabin uses spruce vertical and horizontal parts, and everything aft of the cabin is balsa (the lower longeron has a splice just aft of the cabin where the balsa and spruce meet).