Awesome looking project. Are you concerned about the effectiveness of the dump port on the bottom due to the relatively flat bottom of the keg?
I'm not sure if this is a good reference, but it provides some insight on fermentation vessel design.
Brewing: science and practice - Google Books
See page 514, section 14.3.1:
..."An important characteristic of these vessels is the steep angled cone at the base. An angle of 70* is required to allow the yeast to settle into the base of the vessel at the completion of primary fermentation. This has allowed, in some systems, maturation and conditioning to take place in the same vessel as fermentation"...
I'm not sure that a full 70* is really necessary but it seems like there's a chance you'll leave quite a bit left in the bottom. With occasional agitation (tapping on the outside of the keg?), perhaps it's likely you can get the trub, etc. to migrate to the dump port and using multiple dumps over a few days will result in a good dumpage. I'm not sure. Huh huh, I said dumpage.
I'm building a ss conical at the moment (with the help of a welder friend) and I have a flat plate at the base of the cone which is about 3" wide. I domed it out as much as possible but I'm still a little curious as to whether or not this will allow me to adequately dump. Here are a few pics: