Yeh ive got the permits n spoke with RTA, MVR, DOT QLD, VICROADS and its all sweet. Height is not an issue....look at the 3000 Sailfish, it is 3.8m high on the trailer and in the NT all the power cables are over 5m high...same with all the roads ill be driving due to mining equipment and cattle trucks.
I found out the just make the hulls wider....which is the answer to my question.
BTW if anyone is looking at oversize boats in NT/QLD its 3.5m without escort vehicle and bout $40 for 3 year permit. Goes through same day .