repairing locksmith opened safe?

I have an option to buy an Empire safe, Model # FB-200, that was previously opened by a locksmith. They drilled thru the backside and obtained the combo, 1/4inch hole. What is the best procedure to repair the hole? [other than calling a professional] I have access to various welding equipment. Guessing I should fill the inner part of the hole with say a fire place type caulking/mortar material to help acquire some or most of the original fire rating capability? [if this IS a fire rated safe, still researching] Also, just for curiosity, how does the locksmith acquire the combo thru a 1/4inch hole from the back? Thanks for any help.