Be careful with a press. It can also shoot things out when they're not aligned right. 20 tons pressing down can wreak havoc if something slips.
Did you have four stands under the front and rear frames? If so, there will always be one that floats. You have to put one end or the other under something sprung like the rear axle housing. I still remember the first time I was under a car, bumped against a jackstand, and it moved.