Need help to find unit #

[Sal]

This is my buddy's recently acquired 1990 CHP coupe that I'm putting back together. He bought it as a freshly painted (black) roller that was completely taken apart and was missing mostly everything. Door had vin sticker removed and unit number was sanded off prior to painting. Here's the vin; 1FACP40EXLF170269. It's a confirmed CHP SSP as it has the buck tags in place and the siren bracket was also left. I would like to know how to find the unit number for this vehicle. Any suggestions?