Extra Practice

Past Unreal Conditional - Explanation http://es.slideshare.net/marcaicedo/coruse-15unit-3-the-past-unreal-conditional-inverted-form

Past Unreal Conditionals - Explanation and Practice. This is a great, long, but great exercise ;) http://www.grammar-quizzes.com/condition2b.html  

Past Unreal Conditional -  http://www.englishpage.com/conditional/conditional4.htm

Past Unreal Conditionals - Inverted Form - http://www.daypo.com/test-past-unreal-conditional-inverted-form.html