Lovely painting as eer mate, still the same style as your SOTR stuff, which is very nice and always a pleasure to look at. A version of Matt's rules for a previous salute had alien invaders, (a bit half-life like half-bothered

). That might work. I've found a simple Aliens/colonial marines ruleset that I can email you if you like, (drop me a PM).
There are others out there but can't remember what they're called, I'll check later.
The Commander