The computers in all pumps typically mounted on brackets which could have been heavy steel or cast iron. I would recommend posting a picture of what you have.

Computers can cost $100 to $150 plus shipping. This is an unrestored computer

If you have to get this done on the cheap you can find a way to mount up the face plates and then buy a sheet of computer numbers from a part supply vendor and simply tape them to the backside so the holes are filled. The sheet of numbers is $10-15.