Interesting. I just looked at my truck to see if the support arms might still have had the holes punched in them but they don't. The diagram in the 1948-52 FSM shows a similar photo as your 1947 manual but no spring or holes are present.

Obviously GM felt the springs were superfluous.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)