Hmmm, actually Salman is right that the simplest of conversions should be the 1FZ, but obviously the financial proposition for a 1FZ engine and gear is something to think about.
1UZ vvti (with its auto gear) is available from Haji Zaman in Rawalpindi for around 125k. The auto can be mated on some Prado and Surf gears without any coupling but in all likelihood would need a custom made coupler (which is somewhat more complex than an adapter plate) between the auto gear and the transfer case. I am not sure how lastable this jugaar is, but there is a conversion ongoing on a Land Rover and I will post some pics in a few days....
The 1UZ vvti vs 2UZ is a long discussion, but you are right in terms of there is a trade-off ad the 1UZ is interesting particularly if you are not doing heavy offroading with the rig...
Best of Luck!