Never measured one side by side with a 3dr version, but always found that the side gaps were slightly bigger on RS500 bumpers whenever I tried adjusting them compared to the 3dr version.

The race teams unstitched the front wing lower mounting points on the shells where the bumper also attaches and fitted a spacer to pump out the wing and allow more room for the bigger wheels and tyres and my thoughts always were that the 500 bumper was slightly bigger to accommodate this.

Pretty sure this was why the eggenberger cars were disqualified from the Bathurst win as a standard road car was checked for clearances which brought the practice to light.

Could well be barking up the wrong tree though.