The G body never was sold as a right-hand-drive car, so it would be difficult. There is an Australian on here who has one that has been converted, but it was not easy. He basically used a box off an Aussie car ( Probably a Holden Monaro, Commodore or Torana as they were older RWD Holdens, and Holden is GM of Australia.) and then had to run a cross bar under the dash to actuate the brake pedal. It seems the location of the heater box makes it hard to properly place a master cylinder on the right side. Try finding the thread and see what was written. For my money, I would not do it as it would be a PITA to get used to and it offers no technical advantage. It's not like importing a R34 Nissan Skyline GTR which only came in RHD and is such an amazing car that you don't mind.
If you insist on it, see if a JDM engine importer can get you the steering box off a late model Nissan Navarra, or maybe even a Patrol ( SUV or truck, The Crocodile Hunter drove one on his show). Navarra is the name used in other countries for the Frontier and I know that they use Pitman arm style steering because I have driven one for 9 years. Then again, older Toyota trucks used a pitman arm setup and the Toyota Crown in the 70's was probably set up this way as well. The Crown was Toyota's large RWD flagship and it was powered by a copy of the 1954 Dodge Red Ram Hemi until some time in the 90's. Yet another possible donor would be a Mercedes-Benz W114/115, W123 or W126 chassis car. They too were pitman arm and available worldwide in a variety of models too numerous to mention here so I just put the chassis codes down. Both the Crown and the Benzes were used in taxi fleets so parts should not be too expensive.