I was looking into that way but found a cube to be better for my situations ( my opinion anyhow)
if you run a vice you have to run it horizontal so you really dont have a way to tighten it unless you put a through hole in the tail stock end then a modifed vise handle with extension. theres one made like this I have seen before its around 1500 and will hold a double lock. but then its limited on what you can put in it.
The one thing I dont like about running with a chuck on something that big and heavy is the fixture mayslip when taken heavy cuts, At the very least I would reccomend a 3-5" circle to locate on and cut full dia. pie jaws.
That all being said every application for the use of something like this is different, while it will work for some others it might not.
I personally feel more comfortable with the chuck being gone and bolting directly up to the face plate, to me its more rigid.
I think that fixture you drawn up would work great for mounting a few round parts with collet fixtures on it. mounting any part below centerline would require longer tool holders that would also give off vibration
That is a dam nice solid work job, I like the reflection part, some of you guys can really do some very nice cad work. I suck at it, my 8 year old does a better job with crayons than I can with 3d software.
Not downing your work or Idea at all, as I am going through the same thing, I have one fixture that I am making that has limited use's heck to be honest it would only work on a hand ful of parts, one reason why I am taking so long to build it cause I would like to make it work on lots of different parts that we see. Mine wouldnt work for something like yours would ( which I could use from time to time.) fixtureing is a never ending story, we just never have enough fixtures LOL