I suggest you consult a kitchen contractor or cabinet maker and the granite installer.

I would give a call to have a local fabricator come out and take a look. We can cut on already installed granite, so depending on the situation, it might be an adjustable cutout.

What is the size of the space between the adjacent cabinets to the oven? You must have 30" there. Too little, and you'll have major surgery to move things to fit. Too much and a slide in won't slide in. It'll have gaps.

You'll need a top notch granite fabricator who can contain the dust from cutting in your kitchen. The dust will still be horrible and abrasive to everything it touches, even with containment. It might end up being less damaging, and cheaper to replace the granite than to try to cut it in the kitchen.

What are you planning for ventilation rather than the MW?

What did you end up doing? What you typed originally, sounds like my same issue, even with the same manufacturer of GE Profile. I'm tempted to go with GE Monogram so I don't have to cut the granite countertops. But I wondered if having more options of manufacturers if I went with a slide-in range instead of replacing the gas cooktop and electric oven as they are designed now.