The issue of using the Regency Polaris ADF NC7100,7200 on the Ham bands has been raised on the web a few times over the years. I don't believe anyone has reported on a connection that works. Please report on your efforts if you engineer a way to connect into the DF side. I bought a NC7200 in 1979 for use on a boat. I still have it. It was very advanced at the time, but a few marine channels have changed. It was repaired once by Uniden in Texas who might have bought out Regency. I don't have the service manual. The US Patent office has some block diagrams of the Regency ADF which might help.
The Regency NC6000 ADF adapter is the unit to seek out for ADF use on the ham and VHF public service bands. The NC6000 connects with speaker and antenna cables with FM receiver/transceivers, in other words, plug n play.
The Sitex 525 ADF adapter with a similar antenna is an other sought after plug n play unit that works with 2 meters, also 70cm. If you find a complete working Sitex 525 ADF, antenna, and cables , buy it.