What about the 1840 siege mortar? (Top and bottom pictures of The Jeff's post) Is it an 8" or a 10"? I'm guessing 8", based on trying to get a sense of scale from the confederate Coehorn in the foreground in the bottom picture. The top picture is actually a cross-eyed stereogram - if you can cross your eyes so that your right eye focuses on the left image and vice versa, you get a nice 3-D image. (this takes practice, of course!)
Edit: Duh - I just realized the stereo pair clearly shows "972" stamped on the muzzle. Since the nominal weight of the 8" is 925 lbs, vs. 1800lbs for the 10", it's gotta be the 8"!
andy