Doesn't the first one across and first down have to start with the same letter, if that is the case there are only 3 letters that are used more than once, L E and A, I think!!!!!
The last one across and the last one down would have to end with the same letter too because they meet. So, according to my worn out brain, YIWHR must start the first accross and first down OR end the last down and across because they meet & there is only one of each. Im going crazy but hate quitting