??? Harmonic Balancer for 1966 273 Commando

I've been told that a Harmonic Balancer for 1966 273 Commando is not the same for later, '67 & up 273's. I was told that the numbers are read from the passenger side but as seen in the photo my timing numbers are facing the driver side. The harmonic balancer itself is located more to the passenger side. Checked Jegs & Summit and they list only '67 & up. Any ideas where to get a new replacement or what years would be interchangeable? My 273 only puts out around 285 - 300hp.

Thanks