I was planning to use a Ludwig head steady. Ludwig is the internet name of a very clever German fellow who reduced the weight of his 850 Commando from 425 lbs to 300 lbs and made a lot of improvements. His headsteady design is excellent and it is quite narrow.
I also have room for a MK3 box type with the spring. That was the last version of the Commando head steady and I think it's the best.
Glen