There is no "IF" about it being an option for all USA Chevrolet trucks in 1954 (except for Forward Control & School Bus Chassis).
A similar option called Shade-Lite glass was available in Canadian Chevrolet trucks in 1954 (rear glass not included).
In 1954 (USA prices - Canadian prices were a little less, due to no tinted rear windows):
$18 for 3-window cab
$20 for 5-window cab
$27.50 for Suburban (15 pieces of glass)
(cheaper than rear corner windows)
However, it looks like RPO 399 is not available in 1956 (RPO 398 tinted windows was available in cars in 1956) - so, unless someone has documentation for 1958, guesses are in order.
