what everyone else said.... its expensive and a BIG PAIN IN THE ASS....
but as for swapping out the whole fire wall u dont really need to... this shop in phoenix AZ does RHD conver. all the time... what they basically do is cut out the neccessary holes on the current firewall on the car to match the JDM firewall and then weld shut the old ones... but im sure its more in depth than that but thats what they basically told me when i ask lol