Call you insurance company first, pretend that you don't have a policy with them, and ask about your situation.
That said, if you choose to do nothing, and you get in an accident and they find out about the engine swap they could deny coverage and not file the claim for you. If your car gets stolen they're obviously not going to replace your engine.
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."