Now here's an interesting plate not in any of the known ranges:
Here's another shot of it from
The California Highway Patrolman magazine:
Note the older, straight leg "R" on the deck lid lettering.
I looked up smog history on E436751 and no record found but went back 30 numbers and found all 1991 pickups and utilities starting at E436750. Went forward the same and found all 1992 pickups and utilities starting at E436766. Based on that and it being surrounded by 1991 Crown Vics, I'm guessing this one is a 1991 also. As the possible prototype car for this modification it appears to have been outfitted and plated outside of any other Mustang group. The rest of the lightbar equipped test Mustangs were 1992s most likely produced in a batch from the photos of them I've seen so far (E895220, E895228, E895229).
I'll have to dig through my CHP magazines to find the date of the one I scanned the second shot above from.