I went to a local firm and bought a section and an attached piece that I was missing. This should enable me to finish the through-the-wall installation. Once I've cut away the section of eave above the flue, finishing up the flue and chimney cap should be a breeze.
Once the exterior work if finally done, the interior stovepipe installation should be fairly simple. At least, it'll all be done indoors and a significantly lower height. Then I can clean the cabin up and we can make plans for a winter Yule feast to celebrate our anniversary. :)