This is where the problem lies, "transport" don't often know, and if they do, they won't put the advice they tell you in writing, the most you will get normally is "the information is on the web site" , so you are left to sift through hours of text, and interpret what you read, all with little knowledge to commit to any real legal decisions.
I have personally been through a situation where i rang transport to enquire about compliance/registering a project car i was building, i thought i was smart to ring a few days later to speak to a different person ,and got told the same info, this confirmed the info was correct and so i could continue with my build (or so i thought)
A short time later the car was finished, on presentation to transport, i found the info id been told was in fact wrong, the problems this caused were immense to say the least, the next week was spent between transport and police departments, each bouncing responsibility off each other for the certain aspects i required to get my car on the road.
The bottom line is most people dont wish to break the law, but i feel its so damb hard to actually find out the real legal truth, you just give up out of pure frustration and exhaustion, make the best educated guess you can, and hope you made the right choice, i think engineers and blue plates are still the best option to defend yourself against legal issues, and as a vehicle owner, at least you can't be accused of plain ignorrance !