GE website claims guaranteed fitment when going from 30” electric to gas. We updated from Jenn-air downdraft. The width dimension is good but the depth of the GE Cafe is 20-3/4” vs 22” of the Jenn-air or other similar ones.

I read reviews where someone did the exact same upgrade and they claimed a small gap showed between the rim and granite.

I had to have a granite company cut a 3/4” X 22-3/4” piece of granite And 
glue to the opening so that the cooktop would be supported on the back side.