It seems most Bears like a 8-9" brace height, so I would put it at 8" and do some testing, looking for quietness and lack of hand shock.
I've been using some low stretch stuff like Dynaflight 97 with padded loops on old Bears with no problems. Of course, use at your own risk, but I see no problems so far.
I just put one a '59 Kodiak Special and am impressed with the performance.