given the 1/8" arc height, and the 1 1/4" chord length, we're looking at a
circle with a radius of 1.63" for a stanley #40 camber.

set your caliper to that, and on the back of the blade draw a line square
across the iron 1/16" or so down from the current set of corners.  draw an
arc down the iron from either point where that line intersects the side,
they should cross in the middle of the iron.  then use that point where
they cross as the center to draw the arc of your new blade edge.

bill
felton, ca