OK, you guys are making me want one

I found a very nice '84 RoW Carrera coupe in CA. As I mentioned, it recently had an issue passing smog here in CA and the Euro DME had to be replaced with a US-spec DME and an O2 sensor had to be added. That would seem to imply that the car hadn't been properly federalized before the recent smog attempt, wouldn't it? I'm just not sure what sort of future headaches I'd be in for owning a car like this in California. What sort of things do I need to look out for to make sure it was federalized correctly without any hacks?