Your brace height sounds pretty good for a longbow. Quit bare shafting them! All that can tell you is if you are close on the spine, not if your nock height is correct. Fletch some arrows and adjust the nock height to get them flying well and hitting where you look. Unless you have an unlimited supply of wooden shafts and/or money, you are just wasting both at this point. If the bare shafts group with the fletched arrows, your spine is correct.
Adjust your brace height and or nock placement to obtain good arrow flight and to stike the target.
Are you shooting three under or split? Three under will usually require a higher nock point. You are at a good starting point for your brace height. Somewhere between 6 3/4 and 7 3/4 usually works well with a longbow. My Mahaska likes 7 1/8 to 7 3/8. If I shoot three under, the nock point is about 1/2 inch above the shelf. Shooting split, it is about 1/4 inch above.
When you shoot a fletched arrow, you should just see the fletching spinning, no fishtailing (side to side motion) or porpoising (up and down motion) from the back of the arrow.
I don't find much use in bare shafting wood arrows anyway. I usually just set them up the way I want them and shoot. If they hit where I'm looking, they are good to go. If not, I either add weight or cut them down a bit. If they still won't shoot right, I see how far they will fly with no tip :rolleyes: