Sorry can't really shed any light on Police MVs in general but I have a very old one myself I bought off Spanish Police, a one 'owner' bike I found about six years ago......that's a good ebay find mate are you going to buy it (have you already bought it??)
MV did both 350 and 250 Police bikes. They also did all sorts of other models for the Military, various other police forces and anyone else who would pay. The most famous i suppose are the 300 Raids in military colours etc.
Here is a picture of a restored 250 police bike although without the little panniers they usualy came with. It is one of a matching pair that, i think, Giovanni restored and one is usualy in the MV museum.