Hey Crocdog,
What I usually do with a bunch of mixed up screws is, like you have already done, group them by size. Then, as I go through the guide, I look for places where I remove a certain number of screws at a time. For instance, if I see 4 screws of similar dimensions, I look for places where four similar screws would likely reside. Also, since there is no "official" way to classify head sizes, take a look at [guide|1498|the guide]. When we show to remove screws, you can view the image in high-res and take a good look at the screw heads.
This may not seem like a considerable help, but currently we don't have a better way to correlate screws and guides. However, I have found that a [product|IF145-016|digital caliper] is incredibly useful when measuring screw lengths.