 The lower priced no serial number Greco Les Paul and SG models were made by Cor-Tek (Cort) and usually have Cor-Tek (Cort) potentiometers.The Cor-Tek made Greco guitars have square shaped, brick like nuts with no slope and also often have shielding paint in the pickup and control cavities.Other higher priced no serial Greco Les Paul and SG models were made by Tōkai and the Les Paul models have an EG-75 or EGC-75 model number stamped in the pickup cavity and sometimes have fret edge binding.