lumbersawyer,
The "SPI" label Mike B refers to (Service Parts Identification) data labels for this group of trucks lists all the options the truck would have been built with at the factory.
Take a peek at this
SPI information page along with the last linked web page in the left column.
This should help understand what all that gibberish on the label means by referring to the SPI Code List that describes all the options (at least those known to the owner of the site).
I found 3 different codes on that page that reflect a "4.11 ratio" rear axle. Your initial search/assessment of the vehicles SPI label in question could show you at least what it came with from the factory without getting down in the dirt/weeds.
