Dating a stanley block plane
This sliding seat is machined (on cast iron ones) or stamped with protruding nibs (on the folded steel ones) to engage a series of parallel machined grooves in the backside of the iron.
Thus, a turn of the adjustment knob either pushes forward or pulls backward the iron to regulate the plane's set.
This is the first in a series of low angle (12 degrees) block planes that have the blade adjustment mechanism most of us know and love.
It consists of a knob fixed to a threaded rod, which engages a sliding seat that's either cast iron or folded steel.
Dan The possible mouth plate movement being more than the lever allows is common.
My solution is to use a small chain saw file to modify the slot in the "harp" to allow for more movement.
The black Japanning on the lever cap would indicate a 60-1/2.
According to Patrick Leach, the adjuster was changed to a machine knurled one some time in the 1930s.
This is the only direction that I worry about modifying as full open is usually not as important.
So, either your plane has mixed parts or the type studies may have some errors here and there.
I know of a few, it would not surprise me to learn of more.
The turned up adjusters supposedly started showing up in the 1950's.
Blood & Gore shows a #60 with a turned up throat adjuster and they were supposedly discontinued in 1950.