Back in the 50’s & 60’s Super America & Speedway gas stations were called “Speedway 79”. HERE is a Wiki article on it, but it doesn’t answer my question: What did the “79” mean? Was it for octane?
I have seen it claimed that it was the octane number, but the same person claimed the same for Phillips 66 and Union 76, so my confidence is low.
It might refer to Michigan Highway, route M-79 (my own theory, please be gentle).
On the bottom of this Marathon history page is a link for the complete history of Marathon Oil. Click the link for a pdf document containing this material. It would be a logical conclusion that 79 could be the octane rating. You may have to investigate historical material to know for sure, or do the easy thing and email Marathon.
According to Wiki:
*
Union Oil first introduced “76” gasoline in 1932. The name referred to the American “Spirit of '76,” and was also the octane rating of the gasoline in 1932.*
And:
*
The company that made Phillips 66 gasoline began in 1917 as Phillips Petroleum Company, founded by L.E. Phillips and Frank Phillips, of Bartlesville, Oklahoma. In 1927, the company’s gasoline was being tested on U.S. Highway 66 in Oklahoma, and when it turned out that the car was going 66 miles (106 km) an hour, the company decided to name the new fuel Phillips 66.*
So your source is half right.
Bonus question:
How did cars perform well on such low octane? Many modern cars would run like shit on paltry 76 octane. Did it have something to do with other formulations of the fuel? Lead?
Low compression and timing differences.
Lower octane fuel is prone to ignition much easier.
The downside is that it is harder to hold it off and harder to positively affect the timing. The result is knocking/ predetonation. Not good to ignite when the piston is far from top dead center and ready for the downstroke. That will reduce HP ratings big time (technical term).
So, cars ran, they produced less HP per cubic inch of displacement, and they experienced more knocking/pinging/etc. So, you can use lower octanes, you just don’t get to control the detonation as much and ultimate performance, gained from good timing and compression, cannot be achieved.
ETA: “How did they perform ‘well’…?” Um, they were passable, but the need for power, say in aircraft engines, pushed octane levels up. I wouldn’t say they performed well vs. higher octane engines, but they squeaked out enough power. Cars weren’t scorching the pavement, but they produced adequate results on the lower octane. Planes? Not so much! 
Wait a minute. When was the octane level in gasoline raised because there were some cars in the fifties and sixties (especially the late 60’s) that were scorching the pavement.
The octane level wasn’t raised because of pavement scorching cars, but engines of the era were able to work with significantly increased compression ratios because of the availability of high octane fuels. Look up some of the compression ratios on engines of the muscle car era…
With high-octane leaded fuel, big power was available. High compression, high octane and big displacement engines…
ETA: you don’t make high compression engines and pray for high octane fuels. You build engines around what is available: Lots of cheap, high octane fuel with lead (gets ya some extra valve lubrication, too).
And if you don’t you get the byproducts of detonation, which include perforated pistons. You want to do all you can do to get things blowing up on time.