My confusion comes over the hair. It looks to me like Ben's birth is in the early 60s, and Horace has short hair. When Ben arrives at the island, Horace's hair is above the shoulders, and remains that way until he dies. I'm assuming the hair growth is progressive and he's not getting cuts at the island barbershop.
Now I can't remember, but how long is Horace's hair when Locke encounters him as a ghost building the cabin?
I have a hard time believing the writers are forgetting something. They've been fairly good about sticking to the story and I can't imagine that they're cheating here.
It's just the hair that's tripping me up!