David I have absolutely no idea what the mudflaps or the cars profile looks like, but from your description of the problem, I would be inclined to do the following:
Copy the shape of the mudflaps onto cardboard. (Make cardboard mudflaps basically!).
Then, cut the cardboard ones to the correct profile/shape that will fit. Then, when you are happy with the shape and fit, transfer that shape onto the actual mudflap, which you would then cut and they would hopefully fit just as the cardboard mock-up did.
Just how that will be attached to the car is another matter if the fittings are not in the right place.
Also, I imagine they are pretty tough and won't be easy to cut! So be careful!
