Here's the seamy underbelly; Flue collar to 7-to-6" reducer to tee. Doesn't look like it, but the tee snout is angled up, and the vertical section of the tee is vertical. I probably need to get the bottom support more stable. Full concrete blocks might be better. As you can see, I haven't got the block-off plate installed yet. I went ahead and put the flue damper in as long as I had it, just in case.
(broken link removed to http://i1108.photobucket.com/albums/h407/2bnator/017.jpg)
(broken link removed to http://i1108.photobucket.com/albums/h407/2bnator/017.jpg)