Dont worry mate my car had been off the road for 21 years but i just rebuilt that engine and modified and lets say upgraded i took for mot and it passed went to post office but iam not tax exempt though but what if the engine you put in was already in there and the old keeper never registerd it. i thought all you needed was an mot and logbook to tax it, its free cos of the cars age they are not done on engine size mine is a crossflow it was the same price as a v6 but tax it then phone sort out your logbook to what the actual engine size is cos it will be registerd online as a v6 when they do the mot but not on the certificate but i thought any car that passed an mot was up to road standards if they meet the mot standards whats the worry you should pass the sva but then i thought the sva was if you like made big and i mean big changes to the chassis,