I would use the drill and pin method but i would add this. When you drill out the hole on the side of the horses head make it fit good and tight. cut your brass rod and cover the end in 2 part epoxy ram the rod in and wait for it to set. Now Drill the hole on the neck part of the horse Using a slightly larger drill bit Pack this with epoxy and fit the 2 parts together The larger hole allowes you to wiggle the neck and head together and get a really good fit Use eastic bands, String or even masking tape to tie the 2 parts until they cure I used this meathod when gluing any large parts.