If I were to do such a project I'd probably try to make the weapons swappable with neodynium magnets 
You would think so...

but after hours and hours of work to get everything square and swappable between vehicles.... I realized at this scale it just doesn't really matter. Normally I'm super uptight about this kind of detail, I found no appreciable benefit to having a weapon be one thing over another. To be fair, I try to use as many kit bashed real world stuff as I can, so no lasers, minimal rockets, etc. Mostly mgs of one kind or another, flmaerthrowers, spearguns, this sort of stuff. The real clincher for me was looking at the old Dark Future games the GW people played. Aside from a few of the plastics they had from the box, they used a bunch of hotwheels with glued on weaps. If it was good enough for GW

Just trying to help you avoid the honeypot I got caught in!
Your cars look great! The DF weaps, since they're meant to be futuristic, could conceivably double for anything. We play Outrider and since your weapons are abstracted to a single number, whatever looks great on the model you can go for it!
If you havent seen his page, Evil Cartoonist is a mad genius with this stuff! GOBS of inspiration all over LAF!
Looking forward to seeing how your project evolves!