the problem with using a tapered carb spacer is that it does not allow the retaining fasteners for the carb to apply even pressure on the carb's ears, thus increasing the chance of the ears to break or crack.
this is because the threads are machined perpendicular to the carb mounting point.
the only way for a tapered spacer to be used properly, would be to machine tapered washers that would index correctly to the base fasteners so the retainers would apply uniform clamping pressure on the ears.