Hmm, it was one of the first images in google when I had a quick search:
http://www.raceretro.com/editorialimages/A_2404.jpg
However, now that I look at the image properly, I realise that there is more work done than originally meets the eye
It's not just a case of *donor - paste on bmw parts*

I can see that you've actually kept all of the original shapes angles and perspectives of the base, and changed quite a few parts from the donor, the rear arch being just one example
There is some nice cleaning of some of the base parts too, like the removal of the number plate
You should however avoid being too reliant on one donor image - try and use a mixture, and perhaps change a bit more such as the backdrop and rims, rather than using everything from one image.
That being said it does still look rather cool
