Hey Bobzilla,
As for the sculpt, I really like the original better, this newer more realistic leaner version just doesn't seem to have the same inherent character that Harryhausen created with his puppet. Although, it's a little unfair to judge a few pics to a completed motion picture, but unfair or not, I prefer the original, and maybe because it is the original.

Several times I have tried to copy some of Marcel's puppets, but somewhere along the line, I always stop and then incorporate my own ideas into it, maybe I feel I am not honoring the man if I do a complete take, who knows, I only know that the finished puppet always is more me than Marcel. Having said that, fan films are a hard thing to do, as after all that work, there is very little you can do with them, since you don't own the characters. So my real suggestion is, since you are making a full film, is to make a Ymir like creature, and not a exact copy of someone else's work. Even the shortest film requires a lot of work, so why bother not being able to do something with it when it's done.
Whether you take my advice or not, best of luck with the film, and like the others, would love to see it when it's done.

Tim