A guide for assisting with attachment of a stock prosthetic implant to a patient tissue includes a lower guide surface configured to contact an upper implant surface of the stock prosthetic implant when a lower implant surface of the stock prosthetic implant contacts the patient tissue. An upper guide surface is accessible to a user when the lower guide surface is in contact with the upper implant surface. At least one guiding aperture extends through the guide body between the upper and lower guide surfaces at a predetermined aperture location with respect to the guide body and defines a predetermined target trajectory through the guide body. At least one of the target trajectory and the aperture location of each guiding aperture is preselected responsive to preoperative imaging of the patient tissue. A method of assisting with attachment of a stock prosthetic implant to a patient tissue is also provided.