I remember a friend told me that 285 tires will fit. However, you will need to check.
I would suggest you to hunt for Original OEM Prado mags. Safer and more reliable. Dami na rin kasing nagkalat na replicas in the market so you won't know which is which.
I have 20s installed on my Fort and at 110kph, there is a slight vibration on the steering wheel that cannot be totally eliminated even after 5 times of balancing. As per my friends who also put on 20 inch shoes, ganun daw talaga characteristics of most (not all) China or Taiwan mags sold here. Primary concern kasi these days is budget kaya ang mga binebenta sa market mura na compared to the past where quality is what many are after.