Do you know someone who works for a body shop? If so, see if will allow you to borrow a friction jack to spread the tunnel width. It allows you to move it in very small increments & gives a good feedback as to the amount of force being applied.

In a civilized country, wild animals only continue to exist at all when preserved by sportsmen. The excellent people who protest against all hunting are ignorant of the fact that in reality the genuine sportsman is by all odds the most important factor in keeping wild creatures from total extermination.

Theodore Roosevelt