It seems you have a set of plans from an earlier version, the plans I have do not show this.
I actually prefer a spoiler over a flap.This configuration looks interesting. I will have to study this plan.
See, we are always learning something new.

Mk made the variable pitch prop, no longer available. Even when they were in production they were hard to get.
They were intended for the 2 strokes.

This prop setup, flaps, spoilers were all to slow the plane down to execute certain maneuvers better.