Update again: Well, I decided to try swapping my other silver screw pedals with the PH-1R, and they both worked!
My 78 DS-1 and 79 CE-2 silver screws fit into the PH-1R and vice versa.

The CE-2 had the exact same head shape, so I used that screw for the PH-1R.
It's still a mystery to me. I can only speculate the the PH-1R needed a divorce.from it's original silver screw of 43 years.
