Nope.The 300 is dimensionally larger.Taller/Longer.my understanding is if you try hard enough you can get one in there but its just not easey or cheap.
Back in the 80's. When I worked at NAPA, their was this guy who put a 300 in his maverick and was running low 10's in the 1/4 mile. Really rough looking but it would lay down the rubber like forever.
Someone had said they use the same mounts... just heresay. I don't know for sure. I have seen plenty of pics of the 300 in Mavs. They are very long, and all I have seen required a hood scoop offset to one side of the hood to clear carburation.