This issue has persisted since Forza Motorsport 6. The Shelby GT-350R is probably the most inaccurate Xbox One model in Forza (not counting models based off of Xbox 360 and earlier), despite only a third of its body being the issue.
The entire front end is carried over from the 2014 Mustang GT that debuted in Motorsport 5, and thus it’s significantly too high. This causes the whole front bumper to be stretched to acommodate headlight placement.
Interestingly, the same issue cannot be found on its more powerful sibling, the Shelby GT500
In theory, a simple solution would be to get the front from the GT500 model, apply it on the GT350R model, and then just model a GT350R bumper for it. Really, the rest of the GT350R model is okay, it’s just the front that’s painfully inaccurate.