Leatherworker, I think the buckle you've described as the most recent incarnation (thinner, etc.) is probably going to be the best bet. Out of all the ones I've seen, your last one pictured looks AMAZING. So if this newer one is even thinner and better, you might have the perfect UC2 buckle!
Since the game has been out for years, I think it would be extremely unlikely that any new info, pics, behind the scenes, or anything new pertaining to the game would come to light.
All in all, with your attention to detail and perfection, I'm sure everyone is going to be over the moon when you've completed this new buckle. I know I'm waiting with bated breath!