I have one of these, also purchased new around 1984 with an FD mount, and it's an outstanding lens.

When it came out originally in the 1980s it outperformed the comparable Leitz lens in certain ways. Have you compared it to your FD 100 Macro? I wouldn't be surprised if the Tamron were sharper, though the FD 100 has the attraction of being the only Heliar-type lens in the FD line, which could make it a nice portrait lens (I don't have one myself, so I haven't tested it, but it's an interesting possibility). The Tamron SP90 is a nice portrait lens too, but for different reasons.

A note on the Adaptall mount system--you can find Adaptall-II mounts for most cameras except EOS. Tamron made an Adaptall-II EOS mount briefly, but then stopped in favor of offering only fixed EF-mount AF lenses, so now the Adaptall-II EOS mount is something of a rarity, like the original FD-EOS converter.