The coupe roll center vs the roadster would naturally be higher but the additional weight added by AJ’s roof mod wouldn’t be noticeable unless the car was pushed to its limits as in race conditions and then probably only by a professional driver. As a street car, the difference would be negligible. Swapping the boxer motor for a more conventional I-4 engine would have a similar effect.
The best thing about building an 818 is that you can mod to your heart’s content without feeling you are violating some sort of guidelines as one would have by building a replica of an historical car such as the cobra. I’m anxious to see AJ’s final vision for the car.