From what I read, Hill used round headed milner pins, thin quill, probably wet, to get them flexible, then put 1-pin at the rear, front pin was offset slightly (1/8"), feather straight not helical, rotate pin head toward tip, stretches feather tight. To glue, he used duco cement and put a bead along the outside edge of the quill on both sides. He then tapered the leading edge and added cement to hold it down.
I believe he offset the feathers by sight, but could have used a gauge or pencil lead.
If you have access to Bob Burton's book, he has pictures of several of Hill's arrows and the homemade multi-fletcher that he or someone built to make arrows.