My violin case needed a new handle, so I threw a design together really quickly.

You should be able to scale it a little for different case sizes. I included two pictures of some of the dimensions.

I printed mine at 50% infill and had to sand the inner sides a little - the inner distance was right at 95mm and was a tight fit on my case, so I'd suggest erring a little bit on the larger side if possible.

Angles are all 45° chamfers and the holes for screws are only 5mm, so you should be able to print without supports.