Will this engine Fit

If your G6 has the 3.5L V6 you indicated the 2.4L I4 will not work. You need another 3.5.

Trans-axle, wiring, computer, exhaust, cooling, dash and suspension are all different between those engines.
Plus you really want to avoid an engine from a vehicle involved in a front impact that hard unless you can inspect it before you buy it. Because of the way things fit and how they mount an impact like that can break parts that you need.