Jim went ahead and prepared the wood for painting - first he has sanded it, first by using the coarse sandpaper, then the light grade sandpaper, all the way to the lightest sandpaper.
More on this video here:
This is the question I sought to answer next, by taking the wood, the original painting, and through PHotoshop, trying out different layout scenarios
Here is the first, straightforward one:
The second option is to try to fit more of the dramatic scenery into the canvas, which would mean eliminating some of the information, in this case, the sky so that the drama of the crowds watching takes precedence:
As can be noticed, my demos take the hole of the wood into account. I have to say here that even though I like the fact that there's more painting space and thus more details for the audience (and that's where Turner himself was at one point; at the beginning of the fire he and some art students rented out boats and were out there in the thick of it, sketching, then, when the roof of the building collapsed, everyone inexplicably laughed), I miss the dramatic, awesome sky and am not crazy re how the composition holds up.
The third version also removed information, but this time favouring the sky:
I actually like how this one looks the best, though Jim and others have noted how eliminating the drama of the onlookers is a big mistake.
The fourth version is based on #1, but involves making the decision to artificially extend the entire painting to fit through all the edges:
The advantage is it keeps everything in there - the sky, the audience - and it also makes use of the entire piece of wood. The painted version would obviously look a lot slicker than this quick Photoshop mock-up, but the basic idea is I would extend the sky and the bridge to the right, and the audience to the left. One disadvantage, aside from making stuff up, is that the exposition area is still small. This seems to me a visually more appealing option that just the small square though, or of leaving a lot of wood. Note again where the hole lies.
The fifth version is actually my favourite version - it actually uses the sky version (#3) which was my favourite one due to how much I liked the dramatic sky:
Here I made the #3 option, but extending the bridge as in the previous version, but also expanding the left side, and actually choosing to put all the boat people/rubberneckers/sketchers to the left hand side. In other words, I am redoing the composition, reinventing history, if you will.
I think it looks the best. I will look for feedback from others, either online or in the real world, but I'm pretty sure I will choose to do it this way.