Some food for thoughts:
What i do with this kind of problems:
I download a real life picture(if possible) or a model picture from a full side view.(and many more)
I try to get schematics/diagram or any measurement of the car length wise.
That i upload it to windows 3d builder(every window pc has the program)
With scaling up and down until i have the richt size it is very easy to get all the needed diameters/measurements.
3d builder from windows is not difficult to learn, but it is a very underestimated program, why? here is the deal:
With every object you have 3 chooses to alter, but after every choose you have again 3 chooses----->x10000000???
You can go into detail as small as a nano millimeter.
So it looks like a 3d builder program of nothing, but it can compete with programs as Rhino
If wanted i can make a prestation here in the forum?
With best regards Igor