r does not seem to work when rotating an item in the vehicle grid UI. The fusion reactor has 2x4, while the vehicle has 10x2?

With Bob's warfare there are vehicles with larger spaces, the tank MK2 has 10x4 space.

then this still isnt fixed because it says compatable with mk1 tank...

unfortunately compatibility is listed only by if it's the same grid type. the reactor is filtered for Vehicle, which means all. The other types are for specific types like Cargo wagons, Locomotives, Cars and Tanks etc, so unless I was to add even more definitions and make it even more complicated, that "fix" isn't coming any time soon.