[Dynaco Mk III RCA jacks recommendation]

IMO, dynakitparts.com is the preeminent source for Dynaco restoration.  Here are the jacks: https://www.dynakitparts.com/shop/single-rca-jacks/

No business affiliation.

[preamp]

Should be fine as the Stereo 70 has a 470KΩ input impedance.  Of course, overall success depends upon both the NAD and Stereo 70 being in good working order after so many years.

The other way around - Dynaco PAS with a solid state power amp - might need an adjustment to work well.