In my opinion if you were swapping your n/a engine for the same model then i would not tell anyone as its a direct fit, with a fte engine the looms, engine, stalks etc have to be changed. If you did crash you cant say that you never knew that it was a turbo engine in it as most of it has been swapped over. Im not sure how much the insurance will charge for a sleeper as everyone has different details (postcode, age, number of ncb, etc). Tbh if you want a sleeper do a conversion if not just buy a glanza or a gt as it will save you time, effort and cash in the long term. I have found a link will help you out />http://www.direct.gov.uk/en/Motoring/OwningAVehicle/ChangesToYourRegistrationCertificate/DG_4022054 Shahzad