It's possible that everything could have been swapped. As strange as it may sound, I have heard of V8's being replaced with I6 engines. Obviously not the norm, but it has happened.
Might be some clues to look for on the body to ID some V8 parts like suspension. I noticed there is no seal on the radiator support. Those were typically installed on 6 cyl cars, stapled on.
You could also look for date codes on the 6 cyl parts to see if they coincide with when the car was made.
My guess is the I6 parts were swapped in.