Hi,
Put the new shaft on the cue and feel for eccentricity before you buy it. It may or may not fit perfect. After you put on the new collar you can make subtle changes to the size with the sealer and the finish coats. It would be your choice to live with it if it is a little off.
As an alternative, any competent cue maker should be able to make a shaft for you where the rings match and the weight is close.
Rick G