66 Slant AC Harmonic Balancer question

I don't know what that balancer/pulley is in your hand, but it doesn't look right. When you say "AC condenser" I am assuming you mean "AC Compressor". What you need is the bolt on pulley for the AC, I believe. It bolts right to the front of the pulley that's already there.

Now, please understand I am not very well versed in slants as I usually have pulled them in the past in favor of V8s. But I am building one now for my 64 Valiant that currently has a 170. So, my advice may be flawed.

And oh yes, we need the year make and model of your car. That would help greatly.