Getting to GZ and finding the cache should be the easy part of this puzzle. But you must sign the log in order to count the find. There isn't any trickery here, it is exactly what you think it is - a combination lock box. Please do not damage the container. Once you enter the correct combination, simply depress the button and it should open.
You shouldn't need to disconnect the wire hanger, but if you do so on accident, you must open the latch on the INSIDE of the top in order to put it back in place. Please replace as found, and randomize the digits for the next finder.
There is a easy way to solve this, and a difficult way. It's up to you. It IS possible to open this in one try, if you're paying attention.