Thanks for the comprehensive note.
Particularly
"One early explicit mention is the May1938 CAR 4.532 (b), meant as a certification requirement for ACP (air carrier planes),
"a gyroscopic instrument showing bank and pitch". "
Also, regarding gliders, it now appears to me that there is even today NO explicit requirement for any particular list of instruments to be carried in gliders for flight in IMC or during IFR operations.
Steve