I have no idea how much tranny fluid is in a 4500 PR; but my 4200 HST holds close to 7-gallons, and all I can suggest is have a large container handy to catch the oil. I know, I know...I state the obvious; but changing tranny oil on mine always ends up to be the messiest, most miserable chore of the 200-hour service.
Have fun(?), wear disposable gloves, and keep plenty of rags and oil-dry handy.