I can't speak to the 447 and 448, but the 47 next to a 48 looks like a child's toy next to a tool. While the reach is not that much different, the overall structure is vastly different. The JD rock shaft mount is unbelieveably easy to put on and take off. It is a 2 or 3 minute job both directions.
My suggestion would be to get the biggest implements that JD recommends for your tractor. They won't suggest anything that could cause you problems.