I have put a 1GGTE into one of these. The car was fantastic to drive once completed, and it is a fairly easy conversion. Probably not ideal if you want something to handle well, and it is a very tight fit due to the length of the six cylinder.
Personally if I was doing it again, I would use a 13BT or a 1UZFE. The engine bay is rather large, but would want to do some pretty comprehensive measurements before buying a 1UZ in case it doesn't fit. Note that for all intents and purposes you will be stuck with an auto behind the 1UZ.
Nothing will be a simple conversion, except maybe putting in another 2S. If you have heaps of money I'd say that the 3SGTE is your ideal swap but it's VERY expensive and about as far from 'drop in' as you can get.