From 1947-51, RPO-390 De Luxe Cab Equipment looks like the only way to get the 5-window cab - this option included all the other de luxe cab equipment.

In 1952-53, there were no bright-work options available and the 5-window cab was an option by itself.

In 1954/55, the five window cab was an option by itself AND there were a couple other different de luxe 5-window cab options.

The original question was regarding leather interior covers. In 1949, there was an RPO-361C Leather Trim, Genuine, but the Truck Data Book does not describe the components in this option.