I've found myself buying a few of these maps of late.
A whole series of dozens of them have been re-released,covering swathes of Liverpool, and are very handy in pinpointing old buildings and streets, or to map the changes of an area, over time.
Retailing at about £2.20 at any good book shop.
As for the old Manchester dock. Here's a scan of one of the maps(sorry about the clarity), and as you can see where I've marked in red, the rough footprint of the new museum, which is now built directly over the old Manchester dock.
For those that know your history, sorry. For those that don't. The large George's Dock at the top right of the map, is now where The Royal Liver building, Cunard Building, and The port of Liverpool Building (The Mersey Docks and Harbour Building), now stand.
The dock itself is still there, and was not filled in. The buildings are built on raised pilings, over the top of the dock, and the tide still comes in and out, under the buildings.
Up untill recent years, there was still a boat floating in the dock, under the Liver Building, whick could be glimpsed through the gloom, bobbing up and down on the high tide. When they built the Liver Buildings aproximately 100 years ago, the boat was left in the dock.
In recent years, I think it's finally succumb to rot, and is now no longer visible.