052SI

I think with ever tightening CAFE req's a turbo 6 would be more likely for the GS, I'd imagine even the LS might lose its v8 one day.

iggyhop9

If you look on the Toyota Crown wiki page, the engine choices list two engines that I could see BOTH come to the GS:
3.5 L 2GR-FSE V6 Supercharged (Athlete) (4WD) 380HP
that could be the legit V8 replacement, definitely pushing the car from 0-60 in less than 5.
4.6 L 1UR-FSE V8< BiTurbo (4WD)(TRD) 565HP
that could be your GSF. An absolute monster IMO. In the heavier Crown(Crown is 300 lbs heavier than the GS in base guise), it lists its curb weight at 4177 for the 4.6L unit.
Apparently, these aren't theoretical power mills, as the turbo 4.6 engine was used in the production vehicle from 2008-2012, with 10 less hp.