Welcome to FTE! Looking forward to seeing some pics of those trucks to see the differences. I've seen a few pictures of "utes" which I know is a different thing but not something seen much in the states.
The RHD definitely looks odd (to us, at least ;o), but amazingly interesting. The larger truck has the wider grille like an F-7 or F-8. I've never even seen a picture of any of these trucks before without the lights in the ends of the upper grille bar. Fascinating. If you can post pictures of any tags or marking you can find, that would be helpful.
Bit of trivia... crawl under your standard LHD truck and look at the transmission crossmember and the right side frame rail. It's mirror-image of the left side of the crossmember and frame to allow attachment of the brake master cylinder and pedals for the RHD. Also, look at the passenger side floor and compare it to the driver's side. You'll see that the area where the pedals would go through the floor on the pass side is stamped for the cut out that matches the left side.
Also, reverse the instrument cluster and turn the gauges upside down and you have yourself a RHD cluster.