This issue has persisted since Forza Motorsport 1 on the original Xbox. Despite featuring a different version of the car in that game, the model has not been improved in any way to this day. I understand that this comparison GIF isn’t perfectly alligned, however anyone who has seen both the in-game model and the real life car can attest for the listed inaccuracies. The dimensions are incorrect, the roofline is outrageously wrong, the rear end is completely misshaped, I suppose the roof itself was made for the targa version of this car, but even that one has a different side window line.
While this comparison uses Horizon 5 footage, the model remains unchanged in the new Motorsport, apart from the lights in the front bumper for some reason.
It’s sad to see these classic Ferrari’s be affected by these erroneous car models. The F355 simply put is proportionally wrong with many erroneous details only worsening its look and accuracy. You can find the linked post to this car model in FH5 here to understand the problem,
Just discard this car model and respectfully rescan the vehicle like it deserves.