I guess he just purchased the car, instead.
I have quite a few image editors, but have never really understood how to make any of them do their best. But to my surprise, PhotoFiltre Studio X Pro did a very nice job on this exercise. No painting at all, merely convert to grey-tones, and play with light and contrast - that's all (regarding the body work, obviously)!
I did not have the patience to fix the edges of the grill and the bonnet.
click thumbnail for 800x600:
Apart from the edges, the most of the car is fine, I think. But the more I look at the front, the less I like it; that dirty grey/gray is too ugly and un-real. What would the proper trick be? Too many details already have been lost!
For the sake of backup, for rehearsal purposes, I have saved a copy of the original version:photo alteration, any photoshop expert please?