The previous poster was wrong
There are two versions of the Super-Takumar 1:4 / 150mm according to Gerjan van Oosten:
- Made from 1965-1967: 5 elements in 4 groups
- Made from 1967-1971: 5 elements in 5 groups (P/n 43741)
The first version is somewhat weak at full aperture. The two versions can be distinguished by the size of the rear element: the later version is bigger.
I don't have this lens (yet!) but I'd look at the product number engraved in the Auto/Manual switch. If there isn't any then I think it is the earlier version.
Of course there's also the S-M-C version. This has the same layout as the last Super-Takumar, but with S-M-C coating.