So you are guessing in the end?
For that particular fictional vehicle, yes. The real vehicles are from real specifications (as are the fictional vehicles based off of real vehicles).
and for known vehicles thats all good. But alas my future game does not have those stats to use.
The d20 Menace Manual has Hellfire missiles, sidewinder missiles, a missile platform, and a minigun (page 223). The damage of a hellfire is listed as 15d6 (it weighs 45.5kg/100lb.), the sidewinder as 20d6 (an AIM-9L weighs 85.3kg/188lb.), and the minigun as 4d10.
As for the missiles guidance system, how to resolve missile attacks, missile fuel, and the act of avoiding missiles, I would use the rules in the Star Wars revised core rulebook (page 214 and 215).
For the cannons, I would just extrapolate from the existing damage (but your system doesn’t seem too bad).
I also used the SW core rules, and simplified a bit (in SW they keep attacking, and possibly had speeds all their own. this way, they attack a few times and go home. also, lower tech).
So yeah, what are the typical weapons on the vehicles you already stat'd (not d20 rules so much as just a listing)
Most of the vehicles have more than one armament, but I'll post them when I get a chance...