If you have to ask, you can't do the swap.
The easiest as stated is the 3.0TD out of the diesel 4runners and surfs. And if you can get ahold of Ians at the right price, it is actually not a bad idea. BUT you would have to still be able to wire it in, and i am sure that the steering box and other various other sh1t will need to be moved due to it going from a RHD to a LHD vehicle, and generally for someone asking a question about what diesel motor to swap in on the internet, will not be able to swap a motor.
But, if it were me i would do the 4BT cummins swap which (would need suspension beefing up) should be able to a tranny this will bolt to fairly easily and probably the R150F, or a 1.9 VW TDI either ALH or AHU, but you would need an adapter to get this to fit as it is a FWD motor and it needs to be adapted to a 4wd vehicle. I though have given up on the diesel swap in the 4runner as i would much prefer it in a different vehicle.
In the end though, the swap really won't pay for itself, unless you get the motor cheap, and do all the work yourself, but i do understand that it is not always a monetary reason why people want to do diesel swaps. If you feel you can prove me wrong, by all means do it, cause i would love to watch the swap happen, but these threads come and go, and still there really aren't any diesel 4r's in the US.