That's what it looks like from the picture(s).
The metal piece (in your picture) which attaches to the body and base of the mirror also looks too wide for a 68 mirror. But I'll be the first to admit that there could be some sort of exception. I've just never seen it. Years ago, I did own a 57, but my sister (whom I have forgiven) totaled it.
Let me suggest that you email Bertfam (Ed Bertrand) with the picture and ask him. If the gasket has a part # on it, tell him that, as well. I'm not trying to speak for him (and do not presume to), but I do know he has a P&A that covers 68 parts. I've emailed with him about the P&A. I'd love to find one, but they are expensive!