A 2003 Import won't have a 300bhp engine as standard.
Not sure of all the differences with the HR but I would imagine it is slightly more than just changing the air intake and tweaking the ECU, sure someone more technical can confirm
As for swapping the whole engine for power gains that would be a huge expense for very little return, much better to just remap the car as it is along with a few well chosen mods or sell it and buy an HR