How do you model an object (car) without all the orthographic views? I for example want to model a car, but there is only one perfect orthographic side view and one imperfect front view images. I've got only 2 views and missing 2 views. 

I start to make blueprints (in blender) for the orthographic views but the end result is not as expected and I'm left with blueprints that don't match.
Here for example I tried to make blueprints for the Praga R1R: 


https://imgur.com/t8W67Wt

As you can see, the end result is not nice. I tried to match front view with the side view taking reference points but without success (you can see the back side of the car in the front view which you shouldn't).

I then proceed to start modelling with the help of perspective images of the car, but then give up as I couldn't match the proportions.

What do I do?
Without any references to get accurate dimensions, you can take Artistic License on it. 
Basically just decide upon what you believe the accurate dimensions to be and go off of them and GL.