Have a look at a website called
www.afritackle.co.zaLook at either Doug Swannell Custom Lures or Seal Point plugs.
I live in the republic and these are some of the most used land based lures. Many also used on the boat for yellowfin tuna and yellowtail kingfish.
100m would be considered average for casting distance depending on the gear you are using.
I have fished WA and did very well on long tail tuna, Spanish macks and queen fish off of the cliffs.
If GT is your target look for the wider ones that push a bit more water. They tend to hit short of the lure on the narrower plugs that you wind very quickly. The wider ones will also call fish from deeper water. They are also good for any of the reef dwelling species like coral trout.
Good luck
Let us know how it goes.
Kind regards
Anton