When I'm making shoot shaft arrows I only check spine to find the stiff side, the side that goes against the bow. I then cut the nock accordingly. The natural taper of a shoot shaft allows it so shoot about a 10# range of draw weights. I have also found that shoots of similar material and size shoot similarly.
Shoot shafts have a pretty irregular surface with ups and down, small knots and wiggles. Even with all these irregularities they can be made to shoot well. If they are a little stiff you can sand the mid section to weaken the spine or you can add heavier tip weight and/or leave them longer.