Today I did the cranking compression test. I tested all 8 cylinders, and here are the results:

#1 - 155
#2 - 170
#3 - 165
#4 - 150
#5 - 165
#6 - 165
#7 - 158
#8 - 160

Andy has suggested that I start using a mix of 3 gallons of 100 octane unleaded fuel to 1 gallon of 110 leaded fuel.

One of the cylinders (#4) seemed a little low compared to the others. I need to check the rocker action while cranking the motor to see if there is any visible difference for that cylinder.