Hi guys, new member here. Somewhere here I read about someone having problem opening a Mac box without a lock or key. I myself recently had my MB1700 Series (80's vintage?) lock tumbler unattach itself from the lock rod after 20 plus years of faithful service in the locked position.
The locking rod works by the key and screwed on tumbler by turning and the bent/angled part of the rod turns and lifts a hinged plate and two plates that have tangs that grab the wall of the back of the drawers.
Now there are two ways to open your box and they require some nerves and patience to not destroy your valuable box.
1: Put two wedges between the top drawer and the box frame, like you were trying to see what's inside at both ends basically pushing down on the drawer. The wedges can be wood, plastic, or even two thick screwdrivers. Wedge them in about 4 inches from the ends of the drawer. Here's where the nerves come in, next gently...I repeat gently pry the drawer out with two big flat screwdrivers with steady but gentle and firm pressure. What your doing is carefully popping the drawer from the "tangs" that "lock" the drawer. Once you pop the drawer open, you take it out so you can reach and turn the rod to unlock the other drawers. Remove a few drawers to access the locking mechanism. If you still have the lock or a replacement, reassemble the lock assembly and be sure to use Loctite on the threads to keep the assembly from coming apart again. Reinstall drawers and leave unlocked for 24 hours so Loctite sets up.
2: If you have just a bottom box or remove the top box, in the middle of it on top, right next to the lip, drill a 1/8" to 1/4" hole through the top of box. Then make a sturdy rod with a small "L" at one end and feed it through that hole, turn the rod so that the "L" catches the flat hinge release and pull up. It only needs to be lifted an inch or so, maybe. While holding it up, open your drawers. Then follow the removal of drawers and reassembly instructions.
Using these techniques, I can get into one of these boxes in less than 15 minutes with no damage. The hole method may be better for some if only they know the hole is there for that purpose. As it can be covered many ways.
I hope this helps someone in a similar situation.