i dont think you need to make any modifications if you plan to use 31 tires. people have told me that you can go up to 32 but u will notice that your patrol will be a bit slower and this size is harder to find. if you plan to go 33 with your mq, it will need a suspension or body lift of at least 2 inches. because the tires will hit your fender. so i suggest you stick it out with 31.
another thing. make sure your spare tire is the same size as the tires your using. it may look good to see a big spare but when you need it. u can suffer espensive damage to your defferencials if you use tire of different sizes for a long distanc.