Should still work as it uses the rear axle speed sensor(are you changing rear axle?) and the GEM(module) behind the radio to run the electronic speedometer.
GEM also runs cab electrics like dome lights, power windows, 4WD shifts, battery saver relay, keyless entry, ect.....
Computer is not involved with speedo in 1999
Computer is needed for newer automatic transmissions.
Basically early/mid 1980's and up.
If you are using a manual transmission or you are using 4WD and a transfercsae then you could find one with speedometer cable hook up, most 1997 and earlier had speedo cable hook up but had a Speed sensor in place of the cable, and that transmission mounted speed sensor(VSS) could work by wring it directly to speedometer, by-passing GEM.
If speedo is off because of tire size or axle ratio you just need to change the gear on this speedo cable hook up to match what you have, like the old days