I believe the 1970s MAC boxes were made by MATCO. Are you able to find the model number stamped on the back of the boxes? If you post pictures, there are many members who are very knowledgeable and can help ID the box.
I recently had to get some replacement parts for my box I am working on and had to call the toolbox manufacturing plant out in NY to get the part numbers. They gave me a part number for a basic lock and gave me the option to upgrade to a high security lock if needed. If you need, I can dig up the phone number and extension of the person I was told to contact if I needed anything else.