Abstract: Apparatus and method for locating holes to be drilled in natural bone, such as a scapula at a site for a prosthetic implant component, such as a glenoid component to be affixed to the scapula for providing a bearing for a humeral head in a shoulder prosthesis, the apparatus and method including seating a guide block against the scapula at the site for the glenoid component, the guide block having an upper end and a lower end spaced in a longitudinal direction from the upper end, drilling a first hole in the scapula along a first transverse direction by guiding a drill through a first drill guide bore adjacent the upper end of the guide block and extending in the first transverse direction through the guide block, the guide block including a second drill guide bore adjacent the lower end of the guide block and extending in a second transverse direction through the guide block, inserting a locator pin into the first hole in the scapula, with the locator pin projecting from the guide block along one of the first