I lived in Streamwood Il. in the mid 60's and there was a Sunoco station on Irving Park rd. that had the rotating/pick your octane The 260 was actually close to 108 octane. At the time i was running a 671 Blown sm/blk Chevy w/hilborn inj. in a 1956 T'bird and i used the 260 grade from Sunoco, also set a world record in 1966 in (AHRA) A/Modified Sports at Oswego dragway with the car.
Zip.