Whay you linked is just a barrel nut. You may need an Armourers wrench to get it off. Not sure if the threads on ares are imperial or metric but that will determine what brand rail will fit.
All the best with the wedding. My only tip - pay attention to everything - the whole day goes by in a blur otherwise! Any way, getting married is the easy bit, it's BEING married that takes the work!
If it ever fails, heres a permanent solution, just fitted some today infact
https://www.google.co.uk/search?q=barrel+shims&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb&gfe_rd=cr&ei=DwESVMfBNeyI8Qe9h4HgAQ