Slicing a floor pan...

Getting ready to install a Floorplan but don't want to remove the windshield to do it. What is the best way to slice it for installation? I've seen people go right down the middle front to back. I've seen side to side cuts then I've heard of, but not seen, a puzzle cut. That seems strongest in the end, but since I've not seen one done, I'm not sure. Opinions?

It's a 67+ Floorplan going into a 65 Valiant.