I have never owned one, but have worked on/ driven them in the past. If it were me and this is totally up to me, I would have one with the 1uz V8 in it and just mod that. Although I would not turbo it because I like the power it makes as it is.
If I wanted a classy lexus with the I6 swap I would do it in the IS300, smaller sportier car that weighs much less than the SC or LS series.
Just my .02 and my preference, I am one that thinks the 2JZ is a little over rated, its a fantastic motor, but the 7m or 1JZ could make as much power with less money IMO.