Braceheight of vintage recurve bow?

[robinier]

hallo, i got a Groves Spitfire, a onepiece targetrecurve wih big and heavy wooden riser. The bow is 69" long, weight 33lbs, working recurves. Does anybody know a recommanded braceheight? With 8,5" it seems to draw much less than 33. How high can or should i go, without damaging the bow, which shows no signs of big use. Maybe compairable wih other old, long targetrecurves.
Thanks for help       Michel