I am not a blend pump expert but here are some pictures from a Sunoco book.
Also as a teenager in 1958 I remember the blend pump at a local Sunoco station had 8 spots with the 250 left blank & the 260 was blocked as the pictured pump.
Depending on the marketing area not all grades were available.
The "Priced Below Regular" are signs for the introduction of the 190.

Dave

Sun Blender 1956.jpgSun Blender 1958.jpgSun blend pumps.jpgPriced Below Regular.jpg