Yea, I file them down like a dowel, then shape the outer part to fit the particular arrow. I usually use epoxy to set them in (not so primitive, but it works).
As far as spine goes, I'll pick through a batch and match them as best I can to about 20lbs. Cane is very forgiving in spine due to its continues taper through the shaft. Some may argue that, but it works for me. I have never tried spines at 120lbs in a 50lb bow though.. I have used spine as high as 75 in a 50 pounder with good results. (self bow that is.) My last set that I made was tested at a local shoot with guys shooting bows that ranged in weight from 45 to 70 pounds and the arrows were spined between 50-65 (rivercane), and everyone was impressed with the flight. 5 inch parobolic Wild turkey feathers......Terry