So, last and final shots today (I promise!):
Sharp CE-152 Cassette Recorder, Sharp CE-126P Printer & Cassette Interface and a Sharp PC 1248 (8 KB RAM) - all working perfectly!!
Yes, kids - this is what high-end, battery powered mobile computing looked like in the early 1980s.
So happy I could fix both interfaces today!
@josipretrobits thank you!