I would say near impossible. Nothing is impossible but the hood would need to be extended or the engine cut into the firewall. I6 engines are tall and long and the ES300 body is meant for sideways engines.I agree, wonder how much of a hack job it would take to fit an inline 6 in there?
The V6 used in it is commonly used as a swap for the MR2. It is heavy but reliable and responds well to turbocharging. The Cast Iron block is the same as the Hilux V6 but all other parts are different.