A $4\times 4$ block of numbers is shown. The order of the numbers in the first row is to be reversed. Then the order of the numbers in the second row is to be reversed. Finally, the numbers on each diagonal are to be added. What will be the positive difference between the two diagonal sums?
$\begin{array}{cccc}1& 2& 3& 4\\ 8& 9& 10& 11\\ 15& 16& 17& 18\\ 22& 23& 24& 25\end{array}$