Irvine I wouldn't agree to what you just said.
It was a real pain in the ass with converting the Sunny.
A few item which you need to have in mind:
-the bulkhead between the habitacle and the engine needs to be replaced for a lhd one (reasons: you need heater, steering column passing, etc etc)
-the entire wiring needs to be cut and prolonged from rh to the lh (because all the wiring goes on the right side)
-some of the wiring from the engine needs to bbe prolonged
-abs pump needs to be relocated on the right side
-you need to modify the pannel which holds the screen wipers.........
We can go like this for hours with this conversion
)))))
And now to be on topic......
I think that the car is heavier on the right side because of the engine which sits really close to the right side (left side is the gearbox which is lighter), also the floor of the car has some extra reinforcements on the right side......