Amazon's Kindle Previewer 1.61
To view your MS Word file as nearly as possible as it will be displayed on the Kindle, go to Page Setup and set your page size to be 3.5 wide, 5.1 high, and .25" margin all around.
My Matt the Cat file, in Print Layout View now looks like this:
You might notice that the picture isn't quite wide enough... there is too much white space on either side of it. Let's make it a little wider.
Right click on the picture to cause the Pop-Up Menu to appear, as shown in the picture below:
The tiny menu above the main Pop-Up Menu shows the current size of this photo.
You can see that the photo is not 3.0 inches wide, to match the text. but is only 2.88.
Put your cursor on the tiny up arrow and click several times to increase the number to 3.0.
Above is the result, with the photo being the same width as the text.