Yay, thanks!
Food for thought: The GR/OS invasion at Togoria was bloody close. Far as I recall, it all came down to one duel. Which OS won because a couple folk swarmed one Pub NFU.
And, well, I guess we can say without sounding arrogant that GR is a far weaker faction than SSC (I'm not even sure whether GR has any full-time, dedicated masters left since TJO disassociated itself from them and Mantic left the board). OS is a space-filling empire that eats up map space, but it's not the juggernaut it used to be.
The new invasion
rules aren't a panacea and how they'll work out in practice is another question, but due to them invasions are no longer supposed come down to who wins the most 1x1 duels. And causing ooc drama is supposed to incur penalties.
Allies are restricted because now it's a max of 5 instead of 10, but I don't see that as a bad thing in this case.
Just treat it the same as a skirmish. Or a dominion with opposition (which is what a tier 3 dom will probably turn into anyway).