Adelaide here - played ever since GP1 - and did massive amounts of work on GP2 to "Aussify" it - eventually doing all the Aussie tracks (apart from those done by Glenn Durden, David Hosking, and a couple of others). Also did Touring car cockpits (Ford and Holden) with working MoTec displays for engine revs etc, and David Hosking did a Ford/Holden carshape. Currently trying to do same for GP3 - but need help.
I don't have a copy of GP4 - but as my current computer is only an AMD K6 550 with 64M RAM, I don't think I can run it anyway. Apparently GP4 is not track editor friendly - so you are stuck with the original tracks etc.