I'm creating an inspection drawing for an injection molded part.  There are not that many critical dimensions but I want to include the dimension for total length & width, that could be easily measured with calipers, a sort of overall 'envelope' that contains the part.  However, due to the design and the drafts & fillets added to facilitate molding, I have almost no straight edges to reference from.

The edge I'm trying to dimension to started with a drafted face, then a cylindrical cut, then a lofted cut on the top edge to blend in to curvature of a mating part, finally an edge fillet.  Therefore it's some type of weird spline that's left over.

In the SLDDRW, any way I try to select this edge, I get the message "the selected entity could not be converted into a line or a circular arc".  I've tried smart dimension, vertical dimension, holding shift, etc.  If I go to the SLDPRT and use Evaluate > Measure, I can select this edge either holding shift (although Min Distance behaves but Max Distance still shows me the Min Distance), or I can select the midpoint of the spline but this isn't quite what I want since the spline is not symmetrical so the midpoint is not at the highest/lowest vertical positions.

Any suggestions?  The only thing I can think of is to do a section view along the mid-plane, but this adds an extra view for a dimension that I think is more easily conveyed on the front view and adds unnecessary clutter.

I guess the most generic form of this question that isn't specific to the part I'm dealing with now, is there a way to find the point with the min/max Y position and select it, even if I didn't know where it should theoretically be?  (In this example I know it's on the mid-plane, but there could be scenarios where the min Y and max Y are not on the same vertical plane).

Thanks

[EDIT:  while I'm still curious about the generic form of the question I asked at the end of original post, it seems my current problem may be because this is a silhouette edge (which seem to be problematic), so I'll do some more digging for a solution]