Take a bus from POR to the Magic Kingdom, allow time for the bus to get there. You should be able to catch an early bus, because they run them for people trying to get to early character breakfasts, or I think they do. I don't do anything that early.
If the MK has extra magic hour on the day you are going, the buses will run early anyhow.
Once you are at MK you can either walk over to the monorail station, get on the monorail and ride around to GF, or, weather permitting (and maybe faster) you can take the motor launch (boat) from MK to GF. The launch goes from MK directly to GF.