RE: longbow sights
A little trick ive used with people learning to shoot trad is to;
take a crayon, or something that will wipe off easily from a bow finish. Make a mark on the riser to use as a reference point to line up with the target. adjust just like you would a compound pin. Use your arrow to line up the arrow from left to right. Use your crayon mark to line up top to bottom.
Ive used this method to help people figure out their gap for gap shooting. Ive also used it to help people using both eyes when learing to instinctive shoot. Once you got the idea, just wipe off the mark.