As Kommando said, the spec was what the customer ordered.
Having said that, it would almost certainly have been single carb, with the engine pretty much to A65 Star spec, with an uprated electrical system for the flashing lights, siren, wireless and so on. If it still has the side covers, they will give a good indication as to whether it was single or twin carb. I have a couple of sets of (later) police side covers, and both left covers have a large battery
NSW police bikes used chronometric speedos which were regularly calibrated.
I think, but don't hold me to it, that the South Oz police were the main ones to use BSA twins. I've been told that most of the other states went for Triumphs.
"Retired Fireman" and one of his mates know a lot about the various Aus police models, but I don't think he's been on the forum for some time.
Basically, police accessories are as rare as hen's teeth, so it's probably best to rebuild the engine to 1964 Rocket specs, and use whatever cycle parts came with it. If it comes with police parts, by all means fit what you have. If anybody tells you it's missing such-and-such a part, tell them you haven't been able to find one, and ask if they have any. Surprisingly enough, the answer is sometimes "Yep, I've got one in the shed which was too good to chuck out. You can have it if you like"