re: Massaging the Numbers

Steve, when I am designing curves like that, I like to test them by printing them on paper at full scale and then cut them out so that I can hold them up against the part.  Not sure that Vectric software has that ability but I know that OnShape CAD does.  I am sure that other tools could as well.  You can export your Vectric vectors to a DXF, import it into Onshape and then create a 2D drawing that you can save as a PDF.  Once you have a PDF, you can use Adobe Reader to print it at full scale across multiple pages and tape them together.  You can have Adobe print alignment crosshairs to make it easier to get it taped together.  For your purposes, I would probably tape them to a piece of cardboard before cutting them out to help hold it against the car to see how well you captured and transcribed the shape.   Might save some plywood. 

Let me know if you need some help with the OnShape side.  I could take exported DXFs and create the PDFs in OnShape for you if you want.   And at the end, you would have an OnShape file you could manipulate if you need to.  OnShape is free for personal use.