a guy from another forum had this to say about your idea:
"he may want to wait a little while, the new 4.7 tundra motors are pushing a lot more power stock. from i've heard they are supposed to be putting out an extra 40hp stock or something like that. but from what I can tell the tundra v8 shouldn't be that hard of a swap. I'm pretty sure that with the right electric fan setup and a larger radiator. it really shouldn't be all that bad. it's really nto that much longer of a block"
