A question about caliber 89

Hi everyone, I am a rookie to vintage watches. Recently the iwc caliber 89 interest me, and I did some research online about it. It seems like 89 has different versions, at least different by its looking. I came across a watch on Japan's website, and found this movement has a weird part which is not supposed to be like this I think. Anyone knows the reason? I am quite curious of it. :) here is the link, sorry I don't know how to post the picture directly, since there is no link directly link to the picture but the page. There is a part along with stone which is a kind of black in color compare to other parts. I haven't seen it before during previous research.
www.antiwatchman.com/IP-1756

Unless you understand Japanese and can read the probably very intricate description of how the watch was modified to have a display back, I would stay well clear of this one. It's got more wrong with it than just the mystery black object.
I also doubt the black face is correct.

Be Patient and a good one will come along.

Thanks for reply and advice. It's really hard to understand the Japanese discription by only put them into google translate. It seems that I need more time to do the research. Thanks again for your attention.