As for restoring it... that would depend on if you want a full factory restore. If so then it is not work it. If you want to clean it up, give it a nice coat of paint and use it then it is worth it. If you wanted to sell it you might get a couple hundred for it so putting a lot into making it look nice isn't really worth it.
As for finding the combination or setting a new one:
On each of the inner rings there should be a small line. On my picture you can see it is at 75. This indicates the number.
http://i.imgur.com/dwxqZfy.jpgHere is basically what all the pieces should be in the stack. I don't know the exact model or if it is 3 or 4 numbers so I just grabbed a generic picture.
http://i.imgur.com/YYh66hm.jpgTo find the combination you need to remove the ring/wire around the inner spindle that hold all of the wheels into place. GENTLY spread it out a bit until you can lift one side up and over then remove it.
You need to keep the wheels in order. Sometimes they are marked, sometimes they are not. The first one to come off at the top will be the last one to go back on. There will be spacers/washers and they need to stay in the same place as you took them off.
You simply take each wheel off and mark the number on paper. The top wheel is the last number in the combination. The bottom wheel is the first number of the combination. Once you have all of the numbers and the wheel pack (called a curb) put back together and into the lock you need to dial the combination.
I believe this is a Mosler 10 or 10 1/2 combination lock. They are similar but the different bits are hidden behind the plate on the back of the door. Combination should be 4 numbers and as follows:
DO NOT CLOSE THE DOOR UNTIL YOU HAVE WORKED THE COMBINATION SEVERAL TIMES TO ENSURE IT IS WORKING
1. Turn right stopping when the number comes the 5th time to the mark at the top of the dial ring
2. Turn left stopping when the number comes the 4th time to the mark at the top of the dial ring
3. Turn right stopping when the number comes the 3rd time to the mark at the top of the dial ring
4. Turn left stopping when the number comes the 2n time to the mark at the top of the dial ring
5. Turn right slowly to unlock. Once you hit a certain point it should stop and allow you to turn the safe handle.