Since we are all guessing, my guess is that the plastic backplate was modified to provide clean lines for mounting on a FF model by using the two screws... sort of like the Wasp, Atwoods, etc. were mounted.

Gollywock... a regular Pee Wee was mounted in the Lil Stinker (Pitts). My Pitts is the red/white one. The PeeWee has an aluminum tank instead of red. It was bought in the early seventies.

George