Sad that 2g King springs wound up such a disaster & they were unwilling to accept fault. I remember the problem but hadn't heard the final outcome.
Trimming the Civic drums into hubs to mount disc rotor sounds fairly sensible to me.
Though you probably wouldn't have the centre ring protruding out to locate the wheel centre. (Yes I know wheel studs do that but there is often still a legal requirement for this even if achieved by spacer rings on the wheels).
Longer wheel studs might be needed as well.
Would you have room for the wider rear track?
I have been meaning to look at rear hubs from other cars as well just in case they might work.
I also remembered this thread:
Should I also check costs of buying & posting 2g Prelude setup out from here?
From memory local wrecker would want $35 each for calipers/brackets $20 each for disc rotors, though finding decent thickness discs might be harder & it might be worth your checking cost of buying some new locally? Not sure if Civic/Integra calipers are any different from the Prelude ones but I don't think disc diameter or pads ever changed. Obviously original caliper/bracket couldn't handle the wider track without spacing which might not be a great idea.