245 is the limit of what you MIGHT be able to fit up front, but it will depend on your specific car and the actual tires you use. Just because it says it's a 245 doesn't mean all 245's are the exact same width. Some are slightly wider or narrower than others, depending on the manufacturer and the product line. Also, your car's body may be shifted to one side or the other with respect to the frame, and the body mounts may have sagged over time which can also affect how things fit. Plus, there are subtle differences between the different body styles of G bodies which make fitment different with each car.
IMO, the Regal and Monte Carlo would probably be the most forgiving when it comes to wide tires because of the round wheel arch shape. I think this applies to the GP too, so by deduction, the Cutlass and Malibu are the least forgiving.