What are my options for convergence distances? I only know the options they used for Spitfires and that data is a bit dated and isn’t suited for modern land-based traffic territory incursions. You know, it’s not the Battle of Britain, more Battle of London Bridge. 
I would set them to converge and about 1.5m high at 100m
That gives you anything from from taking out the rear tyres when ‘tailgating’ to filling the cabin with 7.62 at 50m and ‘headshots’ on the driver at 100m 
Sir, you’ve put entirely too much through into this. 
@WarPig Oh, you have no idea how many times I wished that I had twin miniguns instead of a dashcam!
Honestly. Australian drivers have to be the worst in the world. Give me the chaos of Bangkok or Mumbai anyday - lots of horns honking but no-one takes offence and they aren’t driving like they are the only car on the road.
And I have always found driving in the US a joy (once I get used to the wheel on the wrong side of the car) - most everbody is very polite, gives you space, waves you in etc… But that could be because they don’t know if you are packing or not? 
I was going to say 300m zero to maximize your effective range, but honestly for most city driving 1.5m high at 100m like you said is probably dang near perfect.
As far as convergence goes, there’s no way the car is going to stable enough to keep them at the weapons minimal dispersion. I’d hazard (pure SWAG here) an 12" pattern at 100m when mounted on a standard mid sized sedan. So I’d go for about a 12" center of pattern to center of pattern at 100m. What the actual convergence will be would vary based on the bumper width of the carrying platform.
I was kind of visualising a CEP at 100m, something like this:
and this at 50m:
Work the wheel left and right a little bit and cut that sucker in half!
But as @WarPig said. I have probably put too much thought into this
An armed society is a polite society! 
I enjoy driving in Mexico. Everyone is polite and forgiving of Gringos making last-minute lane changes to make an exit, and everyone seems to want to work together to avoid having a collision more than they do here in the states.
Why target the poor unfortunate passenger for the driver’s bad life choices? 
This turn of thread-events suddenly reminded me of a news story from Massachusetts, of all places a few years back:
Yep, I guess we have gone from Visual Jokes to Intensity…
And now for something completely different:
On ops we had a compartment in the drivers door for something beefier than our personal pistols. In my issue car I had an Ingram as an anti ambush/IVCP weapon to give suppresion while trying to drive through. Some had a flash bang mounted under the chasis.
Now there is a story I would like to hear. But if your ‘issue car’ was anything like one that had switches to change the tail light configuration and turn off the brake lights, and looked stock but had a ‘fairly warm’ V8 under the hood. Then I will understand why you can’t 
You may enjoy James Rennies ‘The Operators’. The book has been cleared by UK MOD for release available on Amazon etc.
Oue engines couldnt be V8s because they sounded out of place
Weren’t the range rovers V8s, @Scoop? The quick response vehicles. I may be confusing this with something else my stepdad mentioned. He was over there after you i believe
We only had sedate ‘boring’ cars suitable for sedate boring ‘grey men and women’. Until I rolled it on a bend I drove a Datsun Cherry. You could choose from a list and changed cars often.
Part 2 is also fun:
