There is an AAHS article that gives some details on this never built.
"Late in 1936 Rider decided to construct the R-6 entirely of
plywood for several reasons. All previous Rider racers had had
plywood-covered wooden wings with various types of fuselage
construction. He felt the plywood made it possible to maintain a
more uniform and accurate air foil section throughout the wing
construction. Probably most important, wood workers seemed
more plentiful and easier to recruit. The idea of molding two
very smooth plywood fuselage halves in female concrete molds,
as pioneered by Lockheed with its Vegas, Sirius and Orions,
seemed the ideal route to take.
Rider turned to Story-Gawley, with its vast experience and
equipment for wood working, for advice on the feasibility of
making up the concrete fuselage molds. Somehow, the project
got underway at Story-Gawley, although Rider was still looking
desperately for financial backing for the construction of the
plane. This type of situation was not particularly distressing but
rather the norm for racing plane projects in the depression-
plagued thirties.
When the fuselage molds were completed, there was no
money to pay for the work done by Story-Gawley; consequently,
the molds gathered dust for several months. The stalemate was
broken with the proposal to form the Union Airplane Company.
Based on the R-6 racer, Keith Rider laid out a two-place sport
trainer with possible military sales appeal. By using some inserts,
the existing concrete molds could turn out the proposed sport
trainer fuselages. As the Union Airplane Company, Story-
Gawley would be reimbursed for the cost of the molds from the
prize money earned by the R-6 racer. With hopes of getting the
plane completed in time for the 1937 National Air Races at
Cleveland, construction got underway enthusiastically."
From: The Keith Rider R-6 Behind the Eight Ball - AAHS journal spring 1991
