I forgot to return here (OP is me). In my strange case and video, 3 people minimum did not notice that the Ortofon headshell had a lift arm that protruded higher than the standard Technics headshell. In fact--that was the problem, full stop. I discovered the headshell's arm was dragging on the surface of the dust cover until it progressed far enough the dust cover and headshell no longer had interference with one another. No problem with the SL-1300 works at all.
I am a moron.