Looking at your pics, I would think you could make a better retaining spring out of 3/64" music wire that has the same basic shape but goes
over the hammer pin and
under the trigger pin (opposite what that spring does). The coil on the safety/selector lever would still anchor the spring. Maybe make the hammer tang point down instead of up (or just eliminate it).
The idea of a 'plate' interests me.
I had a side scope mount for one of my AKs that used screws instead of pins. I don't recall how that worked.
It was drilled & tapped for the third pin/screw.