I have just picked up this thread from a general "Google" search on "Tug Canning" and so have registered on the forum to reply. Hence the late response.
I have a large number of original "build" digital photographs of Canning. "Build" in this context meaning directly taken while clambering over the prototype, precisely for the purpose of building a detailed RC steam powered model. In fact two models, one for grandson battery powered at 72 scale and one based on the MMM hull. I also have the full sized builders drawing which a very nice lady at Swansea Maritime Museum copied for me from the original for a fiver.
Sadly the excellent Swanse Maritime Museum has been evolved into a huge and extremely uncomfortable video viewing lounge known as the Museum Of Wales, with most of the original maritime artifacts stored in a shed at Margam. It is still possible to clamber about over the tug with a camera though and the existing boatmen charged with the care of the floating exhibits are extremely helpful.
If you are still seeking information I will happily provide a large file of photographs or if there is sufficient interest from builders I will set up an album on my web server. Brian at MMM thinks this is an excellent idea. I also have a local company who might possibly copy the shipyard drawing at cost for you.
Cheers.
Roy