Valve covers should be the same size, one side will be off-set because 1st, 3rd and 5th cylinders are slightly more forward than 2nd, 4th and 6th cylinders on the opposite side.
I am nowhere near my Bike to see which 3 cylinders (left or right side) sit more forward than the opposite side.
The difference should be the width of the piston shaft collar. Approximately between 3/4" - 1"