Body swap question

Hello everyone, my names Dave and I'm a new member. My question relates to car modification and the legal nightmares attached! 
 I recently had an accident in my 1978 Citroen dyane van. This has resulted in a bent chassis and messed up front end. It is repairable however. I have found a donor car and want to swap the body of my van onto the replacement rolling chassis. The only worry I have is that I would be attaching a commercial van body onto a saloon car chassis ( the 2cv, dyane, acadiane van chassis are all the same) in the eyes of the DGT log books. My van is described as a Dyane 6, "commercial" on the technical inspection certificate. Is this a problem that will result in meltdown at my local ITV centre? What ids the best way to approach this problem? Any answers gratefully received!!