Thanks for the feedback! The elastic gore was the part that had me concerned, so I am glad I asked.
I looked at Imperial Boots, but the sizing on their boots stops at 12 and I wear a 13E.
I saw that TK Boots had the possibility of 13E boots in stock, so I emailed to ask about availability. I mentioned that I planned to dye them black, but was told to just search the internet for black UK chelsea boots.
I guess it's back to the drawing board. Thanks again.