Regarding determining whether the proposed Kitchenaid unit will fit the current cut out:
According to each unit's spec sheet if I am reading correctly:
Existing Whirlpool 30" model SC8720EDB-2 unit rough cut out dimensions are:
28 7/8" wide x 20 15/16" deep
Proposed Kitchenaid 30" model KCGD500GSS rough cut out dimensions are:
28 5/8" wide x 19 15/16" deep
If I am reading the cut out dimensions for each correctly, the proposed unit requires a smaller cut out so the question is will the overall outside to outside dimensions be sufficient for the unit to sit securely on the counter top with no gap around the perimeter.