Consider the following answer, as quoted Shine.
Differences
1. Tail. Long-tail dress Kate is more than 2 meters and is decorated with piles of handmade lace embroidery. Meanwhile, Grace's tail wear silk dresses, lace, and taffeta confection (not hand made) from MGM with wardobe designer Helen Rose.
2. Crown. Grace put her veil on the crown beaded Juliet works fine. Meanwhile, Kate veil attached to the Cartier tiara lent to the Queen of England for him.
3. Volume gown. Without layers of taffeta as used Grace, she looks slim with the silhouette of her dress. Grace alone makes it a little dress "contains".
4. Neck. V shape neckline dress Kate deeper, making the dress look more modern and sexy than Grace neckline that makes it like a choke with a full button up to the neck (swan neckline).
5. Hair. Kate let her hair loose to create a natural appearance overall. Meanwhile, Grace did her hair in a "tight" and neat with a bun.
6. Buttons. Kate's wedding dress buttons located on the back of the dress buttons while Grace was placed from the breast until almost to the neck.
Similarity
1. Lace sleeves. Kate seems to steal inspiration from the dress Grace, because of the similarity-based arm lace dress she wore on so similar. In this way, both designs can be said is almost identical. Inspiration transparent lace sleeves a la Grace Kelly did have dicontek many celebrity brides, including recently, Ivanka Trump.
2. Waist. Kate and Grace are both showing off slim waist with a tight waist line, also for the effect of beautiful and sexy.