The grinding will cause sparks so I would be in favour of sawing, this can depend on the tools you have though & whether you take the bumper of or not (It's always better to be safe than sorry
), people manage it without taking it off though, just be very careful
.
As "lookalikeJCW" says it's better to get a proper fitting one, the slipping the piece of pipe over the thinner diameter exhaust pipe is what I do to get a snug fit, when people have come to me after buying the larger diameter chrome ends, and then can't get them to fit properly
.