Major update: The sample barrels, springs and flippers have arrived! They all appear to be very good quality and the correct materials for this project.
After some brief testing the flippers work! This is a major relief that the plastic might not prove correct. The new flippers convey key presses firmly and accurately as well as the originals, from my initial testing (of course extensive testing will be done after the full prototypes arrive). The new springs are also excellent and require the same amount of force to buckle as original Model F springs. They fit on the flippers well.
Unfortunately the barrels will need a few 0.1 mm adjustments in the molds before they are excellent (the insides of the new barrels require a little more room to match the originals). I filed down one sample barrel 0.1 mm in the needed areas to correct this issue and the new barrel is just as smooth in operation as the originals. This will likely cause a delay in the project unfortunately.
To show how similar my units are to the originals, in the photos I have included a mix of original barrels/flippers/springs as well as the reproductions that arrived today.
Can you tell which ones in the photos are originals and which ones are the new ones?