Prado vs. 80
Regardless of the driving characteristics, the 80 would be a great rig for this trip... The diesels are indiestructable and more relaible than the gas engines, especially on the crap gas you can get on your route.
If you are not a power guy, I'd go with the 1HZ engine as they are probably toyota's most reliable diesel and still in production so part availability is great. you can also turbo it easily and get the best of both worlds.
As long as you are doing the swap, try to get one with the 5 speed too!
K