Looks like this is one of the bits made from Unobtainium, a 8 valve cylinder head for the CB450.
A decade ago I did some serious investigations, trying to get get in contact with, what I believe was, the last man standing, that was involved in making this conversion kit. I have to say I came pretty close, but...
Last year I made another attempt approaching from another angle, so to say. Seems like guys that could help are not interested in helping at all. Ignorant is the word.
Anyway, this is what I was searching for.