Dave
The IS300 is a 6 cylinder in-line engine - 2JZ-GE - the non-turbo version of the awesome 2JZ-GTE from the Supras.
I have fitted the 1JZ-GTE engine into an IS200. This is the 2.5litre version of the Supra motor.
Makes for a very fast IS200 car but was a little expensive to do the conversion. For instance the gearbox also has to be replaced as the engine has too much power for the standard box.
Regards
Graham