I would go the easy route....

Unless you can provide receipts for the mods done to the car I would...
Strip the car of mods while its still in your possession. DO IT NOW !!!

The other party's insurance can then pay out market value on the a standard GX.

Anything else will be a bloody headache.

Good Luck.

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"You can turn your back on a person, but, never turn your back on a drug. Especially when it's waving a razor-sharp hunting knife in your eye." - Raoul Duke