I've always pictured a bomber jacket, but with a little bit more flair. More zippers, a little more structure to the shoulders and waist, that kind of thing. Unlike bombers, who generally needed the extra wool to stay warm, Spitfire pilots generally needed something with a little more room for maneuverability. So I also see a little less thickness to the jacket. Though I like the wool touches, so I leave them in, just not as thick.
It's actually a pretty perfect jacket for Seattle, I think. Waterproof, warm when you need it to be, and cool when you want.