Today's tankers drain much better than they did in the 70's. If you look at the discharge lines, they have much more slope. This was mandated by the shift to unleaded gas in Sept 1975. A gallon of leaded in 1000 was considered too much. Todays tankers drain completely. This is also necessary because of the switch from low sulfur Diesel <500 to <15 ULSD. It doesn't take much low sulfur to make a sample go over 15 ppm. I was able to get leaded gas out of the refinery in Big Spring, TX until the early 90's. Until 1998 I splashed in lead substitute, but that became illegal about then. All additives now have to be injected. There isn't much demand for that type of fuel because in the past 12 years, most vehicles that required leaded gas have became play toys anyway. The octane rating we now post in the US is an average of motor octane and research octane. Octane ratings jumped drastically during the 50's going from 75 to 100 in 10 years. And it varied from region, higher altitudes requiring lower octane. In in answer to the original question, yes 50's 6 cylinders will run fine on 87 octane.
