Lesson #1: Process your own deer!!
Lesson #2: Any cape can be used on a mount with any antlers. Use another cape to have your mount made, it's not exactly the same, but it's still special and unique. I have a friend with many mounts this way and they all look great.
Also, sitting out isn't good and neither is a rotten smell, but let your taxidermist have the last word to be sure. Maybe you did this, though.