Only hassle nowadays is Sean if you advertise it for sale as something like a "genuine original HQ Sandman" or other such cliché'd words there are legal precedents that can come back to bite you. Plus technically it is considered an illegal act to remove and/or re-affix the ADR tag, which if you get hassled in a Civil case for the false advertising you are also likely to be persued for the Criminal act of tag swapping.

So whilst I agree it is OK to use another body, best bet is to use the right body ie right series, right assembly plant (and eg don't use an early 1974 HQ van body for a late 1974 HQ), and when you go to sell it just for example advertise as a HQ ute or van, or if you want say the shell was changed but the right one was used. This way there is no false advertising claim. Anyone selling a car they don't 100% know the history of should probably do the same/similar.