All cars to the best of my knowledge have the Stradale type centre tub, the wheel arch extensions are bolt or rivet on in the case of either of the Gp 4 arch conversions.
It could simply be a swap to a different rear arch design following accident damage or even in the quest for a little more rear suspension travel but the different body style combined with a different registration could suggest a second car is a possibility.
The rear wheel looks to be a TMB racing version as used by Tom & Enzo on here.
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