Marking the blade for the cut was one of the hardest steps. I decided to mock up the assembly using sticks of wood.

The long horizontal piece represents the proposed center of the Vee plow.

The short horizontal piece is determining the width of the Vee plow, or, more accurately, half the width shown here.

The vertical piece on the left is a plumb line.

With all of these wooden lines in place, I traced a line on the blade that was in the same plane as the long horizontal piece as well as the plumb line.