Tips for passing emissions in my '88 Chrysler Fifth Avenue

I know it's not an A-body but it's close and it does have a 318 lol. The problem is the CO readings are too high. It still has the factory "Electronic Spark Control" (quasi-Lean-Burn) computer on it and the Holley 2-bbl with the weird solenoid valve inside. It runs perfectly so for now I just want it to pass so I can gut the exhaust and swap over my shorty headers and make some duals (with new dual cats of course). I'm pretty sure the reason it's failing is due to the cats being old but talking to the mechanic I bought it from he said it tends to run rich once it's warmed up and goes into "closed loop" mode... the second time I took it in after putting some ethanol treatment in the gas and topping it off with 1/3 tank premium (rest was regular in there) and the CO readings dropped drastically but it still failed by only 1.6xx ppm which annoyed the heck out of me but it's all automated so "tough beans". I had also disconnected a small ported vacuum line which I guess helped lean it out at cruise a bit too, just needs a bit more leaning-out I think...??