I wasn't being a snob or anything, just saying I wouldn't recommend doing it. (I don't have EVERYTHING on my car declared; such as interior bits and bobs, but everything substantial - suspension, exhaust etc is covered) And pretty sure you're supposed to let the DVLA know of a new engine too as your logbook has the engine number, so if you changed the engine the logbook would no longer be relevant to the car surely? Bit like you'd have to let them know if you painted it a different colour etc. Tis stealthy enough that could get away with it in regards to Police probably not noticing if they checked the car if you were to be pulled over as looks the same is you just take the 5efe sticker off the cambelt cover. Plus regarding the not big enough to warrant declaring it, officially speaking, you're supposed to even declare optional parts that are chosen for the car when new. (for example someone buying a new car decides to pay extra and have a spoiler or nicer wheels, then they're supposed to declare thse optional parts to their insurers, although I'll admit most people don't)