Rego for tipper/prime mover

Hi everyone, I was wondering what the situation is when you have a tandem tipper with a quick release body that converts to prime mover as regards rego. How, or more accurately do you choose what class to rego? This is a Victorian question but I guess the new National rules cover this as well.

Mark, I'm pretty sure Vicroads will make an executive Decision in their favour.........LOL...

here in N.S.W. you would have to pay Prime Mover rego, & their is a Shape code for being Interchangable between 2 different cofigurations.. that is put on the Rego papers..