Installing front sub frame rail

Is your existing frame rail solid? Not rusted? If so, I wouldn't be too quick to start cutting and replacing until you have a frame shop take a look at it- they should be able to pull that back to spec without too much trouble, hard to say for sure from the pic but definitely worth checking with them. And it will all be square... unless you have some frame rot, then you're back to replacement. The frame shop will have the factory specs, which are also in the factory body & frame manual.