Porsche went to great efforts to diguise prototypes, this 928 test mule in 1974 was disguised as an Audi 100

https://rennlist.com/forums/928-forum/1041136-anyone-recognize-this-book.html

the Audi 100 Coupe body shown in the exhibition was actually much wider than the 100 Coupé from Audi. In comparison, the normal 100 would look like a smaller version of it. At Audi, the Coupe body had been modified in the development department to match the chassis of the upcoming Porsche 928, which meant that it was RWD. The V8 engine under the bonnet had a displacement of 5.4L and produced 350 horsepower. The present-day oldtimer was thus an inconspicuous prototype and could carry out the trials without being recognized by the Erlkönig photographers with ease.

https://www.carthrottle.com/post/w63rlmk/

https://www.roadandtrack.com/car-culture/car-design/a27007948/porsche-928-development-mules-audi-100-coupe/