Kudos to both of you for the effort.  I grew up as an architect using
a pencil but I have been using AutoCAD for 25 years.  John Tuttle's
drawing is all very well but the curve needs to be defined.  Ralph
Nielsen's comments are all very well but the curve needs to be defined.
I've only seen one (mine) while it was in my rebuilder's hands.

With any kind of luck, the curve is the segment of a circle and can
be measured by overlaying your circle template (pencil-driving guys,
remember those?)  With any kind of luck, the draftsman who made the
templates for the manufacturer in Rochester used circle segments, too.
It's possible that the curve can be found using an ellipse template
or <horrors!> a French Curve.

Lacking luck, make a series of measurements of width and I or someone
can draft the points, connect the segments with a 'pline' and command
'fitcurve' in AutoCAD.  It's easy to share a .pdf, .dxf or even a .dwg
file of the drawing.  CNC guys could use the AutoCAD .dwg file and
mill the shape.

Douglas Heckrotte
Philadelphia, Pennsylvania
dheckrotte@gmail.com.geentroep