When I was young I read a book about a boy who found a viking ship in a shop, (one that fit in your hand). He later discovered that the ship could become big, and could transport himself and his friend to other places and times. Also if then ran there hands over the bow of the ship, they would change into the clothes of the period to blend in. They went on lots of adventures this way.
Ring any bells ?. I would love to find this out, as I loved this book as a child