Hi there ,,, for what it's worth , My old titled 1958 scooter had the early style spring tensioner pully and the early style bolt on smaller diameter rear wheel pulley , I remember it also having the 150 cc decal on the headlight shell and the 150 cc cylinder and piston, ( I remember ordering rings from Hastings corp. the size was 2 3/16 by 5/64 ) I can"t for the life of me tell you why that stayed in my brain !! I sold the scooter to a fellow on California named Bill Powell. ( I think maybe 1973 ) Best wishes on your project