Whether you want to install a part-time kit will depend on how you want to use it. The NP203 full-time has been very popular for plow trucks and maintenance trucks because they maneuver better in the snow in AWD, and can switch to 4WD whenever needed. The differential in the transfer case allows it to drive all four wheels on a hard surface without binding. Thats very useful when plowing a parking lot and driving on and off hard surfaces.
The NP203 is chain-driven, but a very strong chain-driven case. However, trucks of this vintage had really bad gas mileage and the part-time conversion was very popular as an effort to get a little better mileage. In general, the part-time kit makes the NP203 a little less reliable because it changes the way oil is circulated in the case when in 2WD mode. You need to run it in 4WD periodically to keep it properly lubricated.
Bruce