The Race will be run at this new blog - http://amazingmutantrace3.blogspot.com/
Anyone can play. If you'd like to participate, visit the blog. There is a link there to an e-mail address you can send an invite request to.
Each player will select an X-Men for their partner. Detailed instructions will be at the Race site.
Once you've accepted the invite and joined that blog, post a comment claiming the X-Men you will be using for your partner. So far I don't see any conflicts in anyone's choices, but the first to call a particular mutant has priority.