Outer Limits 4x4 Board

can someone tell me the best way to get downward travel, do i need drop boxes i have checked out third's arms and told they are not legal in qld and that drop boxes can be engineer approved . Are there any other choices ?
Trying to get all this ready before easter and just want to know the most practical way .

bru21 has 3rds I was under the impression they are ok but have being known to be wrong. i run drop boxes and the work well, put the buch at a better angle so allows freer flex but dont get them OR arms for a miricle, there is only so much flex to had from a radius arm set up