Hi,
What exactly do you mean by low density? The specific gravity? Or, the growth rings are far apart? If it's a good piece of yew, like you say, and you plan on backing it with hickory, it should make a fine bow. If you want 100+#, keep it long, and make it bend full circle. Horn nocks would probably be a good idea as well, although, with the hickory back, it would be OK without them. Good luck!