I'm sure it would drive very differently to an RS200. The 2jz-ge has very different characteristics to the peaky 3s-ge - it makes similar power, but at lower revs and with more torque across the range - it will be much more civilised and less sporty feeling. The 2jz is a lot heavier than the 3s-ge, so that will eat a bit of the acceleration performance, and won't do the handling/balance any good either, as the extra weight is well forward.
I never knew they made a manual IS300, but it will have the w55 gearbox - the RS200 gearbox probably wouldn't like the torque output of the 2jz. They could have used the V160/1 box to make it a 6 speed, but that would have been an expensive option for Toyota, and wouldn't really be any advantage - the wide torque spread of the 2jz only needs 5 gears to be flexible enough.