Note that the octane rating systems have changed since the days of the 260 pumps in the 60's-70's; in those days, only the "Research Octane" (RON) number was used, not the lower "Motor Octane" (MON)number. 260 was rated at 102-103 octane by the "Research" method, and 95 octane by the (seldom-used) "Motor" method.
L-88 Corvettes had 12.5:1 compression, and had a sticker on the shift console that said that fuel used must be a minimum of 103 Research Octane or 95 Motor Octane or engine damage could result (from detonation).
In today's world, fuels are identified on the pump by the new "Pump Octane" (PON) number, which adds the RON octane number and the MON octane number together and divides by two (RON + MON/2). If you could buy 260 today, the pump would show 99 octane (103 + 95/2).
Good premium fuel back in the day was rated at 97-98 octane by the "Research" method, and at 88 octane by the "Motor" method; with today's mandated PON pump-octane formula, that converts to a 93 octane PON number that would be on the pump today. Today's 93 octane fuel is the same as yesterday's 97-98 octane fuel; you'll find 98 octane on the premium pump in Europe today, as they only use the "Research" octane number on the pump.
When we built our retirement home/garage in 2000, my wife bought me a restored Sunoco 260 dial-your-octane pump as a housewarming gift for the garage, but she forgot the 8,000-gallon underground tank full of 260 to go with it.