Hardinge sold 5" chucks for use on their lathes, and that is a pretty good fit, though a 6" chuck works fine. In the last twenty years or so, they also sold 6" chucks, which I think is the best size for the 11" swing HLV-H.
The chuck size you buy is probably a matter of what sort of work is expected, but I like to be ready for both large and small work. I personally use a pair of Pratt Burnerd 6" Setrite chucks, 3-jaw and 6-jaw, on my 9" Hardinge lathes. I never run the jaws far enough out of the chuck body to bang into the bed, and don't suppose anyone would do anything that foolish. I also have a pair of Buck 4" Ajust-Tru chucks, 3-jaw and 6-jaw, mounted on 5C fixture plates that I find very useful for small work.
I have a good selection of chucks for sale. I do have a new Pratt-Burnerd steel body 6" 3-jaw Setrite and a new BTC 6" Zero Set 3-jaw. I have a few Hardinge taper back plates for them, but don't recall if any are unused. I have a dozen or so used chucks, including a very nice "Hardinge made by Buck" 6" Ajust-Tru.
Email: lvanice at comcast.net
Larry