The first suggestion that i have is that you fill in your location detail in your profile so that we can see which country you live in & perhaps offer you advice for the region you are in.

As for your car, with a piddling 38,000 k [less than 24,000miles], hell, it's practicaly new. As long as everything is in good servicable condition, you should be able to drive it round the world with only regular servicing & maintainance.

I don't think that you should be taking on a 500 k trip as a non stop exercise as this would be a five hour journey at an absolute minimum, & you should be pulling up for a pit-stop & a break at least once along the way. Preferably about half way.

I could stretch my old 1200 ute out to a little over 400 k [250 miles] per tankfull when i had the GX & five speed in it, but it has a smallish tank, so you should be able to duplicate this without too much effort.

Happy Datsun motoring.