...land cruiser fj70? if posible, should I replace diferentials and transmition as well?

Anything is posible if you throw enough money at a problem.

I am not entirely familiar with he fj70 series. A good place to ask is www.ih8mud.com it is probably the largest land cruiser community on the internet and some one there is sure to know.

Seems like an odd swap though, If you want to keep it all Toyota, a 4.7 v-8 from the first generation of tundras might be easier to come by than the fairly new 4.0 v-6. the v-8 will run just fine on regular unleaded day in and day out, the 4.0 is strongly recommended to run on premium only. and the v-8, although not making much more horse power will have more low rpm grunt than the v-6.

Good luck in what ever you decide.