If you mean the chassis, then someone on here with a coupe said the chassis is different on the coupe although I am not convinced myself.
As for a V6 406 saloon, the chassis will be the same but other components may be uprated ,due to the heavy engine, like anti roll bars, maybe wishbones, ball joints etc.
Cars in my care:
2021 Kia Spottage 1.6 Pez Turbo Dual Clutch Gearbox Trickery
2013 Renner Twingo - donkey work