I thought this was kind of cool, it really displays the difference in the roof lines.

 

The coupe is a 6cyl.

 

 

Notice the ride height in all of those pics. The rear sits lower than the front from the factory.

 

Mine is the opposite.

 

What you are seeing in the first ad is true artistry. These are the same car. Mostly the fastback. The coupe and fastback were photographed sitting still in a studio and then the wheels on the fastback were airbrushed to make it look like they are turning. Likely the roof of the coupe was cut out and pasted on the fastback photo. The coupe was then airbrushed to soften the lines so it would not look as fast. Most likely this is when the 289 emblem was removed. The side trim was also cut from the coupe and pasted onto the fastback with the coupe roof.
This was in the days before Photoshop. When I say cut I mean with an Xacto knife. Airbrushed means a real airbrush with real paint.
Even the girl is the same. Check out her arm. They added a little more shadow under the arm on the door in the coupe. I am not sure which version of her face was altered, probably the coupe.
"Both" cars were then pasted into the same background in slightly different positions. The shadow under the car is airbrushed.
There are a at least a half dozen places you can find the identical components. I have attached the rear wheels from both cars here. They rotated one slightly so I rotated it back. Compare the circled area to the same area on the second wheel. The differences in lighting is mostly just the scan.
This is how I created advertising in the 80s. Physically cutting and pasting and painting. I was pretty good at it but not this good. This is good work. Now, Photoshop makes it easy.

 

I never would have guessed, I figured they just switched cars and kept driving around the block. Are the subtle differences to make it appear that way?

 

Putting it in exactly the same place in the background would probably have been too obvious. If you want to see funny car ads check out somthing from the 20s and 30s. They made the people about 3/4 size to make the cars look bigger.
Most of those were drawings but some were doctored photos.
Being in advertising so many years I know all the sneaky tricks.

 

HGC,

The best ad is in your signature panel!