Sorry for the lack of detail in the SBS but I accidentally merged the file before saving. Duh! Basically I cut various components from the two cars, and did a lot of warping and re-shaping to make them fit the lemon.
Also a bit of dodge and burn to make it a bit more shapely.
step 2 of 3
Pasted the merged car onto the resized background, added a grey overlay on the windows, and some shadow on the car and ground to make it blend better
step 3 of 3
Finally warped the images seen through the car windows a little, and added a brown overlay over the car - again just to make it fit a bit better with the background.