560's have a distributor cover... while the 500's didn't. 560's also had dual snorkels on the airbox... while 500's only had one. Another good sign was mentioned... the valve covers. Starting 1986, the M117 recieved black valve covers. Earlier, they were silver. No 560 motor was made before 1986(well, some very late 1985's were made) and finding a 500 motor in the US thats from a 1986+ is like hens' teeth.