Hal was a stickler for accurate detail whenever possible. One of things that bothered him was the aileron controls. On the T-28 there is no visible aileron control horn yet on Dave Platt's plans an external horn is used for controlling the aileron movement, so the horn and the linkage are visible. Hal made a mock up of an idea he had to incorporate the control completely inside the wing and aileron as it is on the real T-28.
The following drawings show the mock up he made: