I used a Hasbro Anakin Skywalker figure from the Phantom Menace and I feel the size worked out. Though the neck post wasnt quite the right size. Here are some pics. Sorry I'm having a hard time finding better pics of mine at the moment.
I painted it, but its from Lonnie Hale Hero Heads. I contacted Lonnie through sending an email to [email protected] and got set up with a Short Round Head that way. Good luck with your project!