i had a 94 3slow with high hc and nox, chances are you will need a cat and o2 cuz of the blown hgs, but really check out the egr set up, vacuum lines, egr valve, egr vacuum modulator, i was blowing double the limit on hcs and nox on mine put in a new cat,02sensor and a new egr vac modulator, Problem solve. and it only cost me about $300 buck
picture below is what was wrong on my 3slow egr vacuum modulator/ egr transducer

 

I have one of those EGR Vacuum Modulator in my Trash Can... If they are the same you are more than welcome to it for cost of shipping it to you. I live in a state where they don't test so those systems have been bypassed on my truck.

I have a 1991 3.0 so check parts numbers between the 2 trucks. (not even sure if it works) just offering it if it will help.

 

you also can check if the cats working by checking the temp of the exhaust pipe going into cat vs going out. if its bad pipe will be hotter going in than out, infared temp guns are awsome

 

Yea a buddy did this test with a infared temp. gun. Numbers were inconsistent. Anyways I did my retest today with a new cat and o2 sensor and it dropped all number by a whole lot. After investing $500 it better pass. I guess it's double the price paying a smog tech but atleast I did it the right way. Thanks guys.