Easiest ways to fix codes P0402 and P0420?

[Scotty-Z]

I've been tracing down gremlins for months with this damn car after finding out that my plates were expired (I told them 2 year plates, dammit). One problem was traced back to the PCM, another was catalytic converters, and another was a chip that had been installed by a previous owner. Haven't had the money to keep throwing parts at this thing, but it's my only vehicle so obviously it was my only way around. Got pulled over a week ago for the expired plates and need to get this stuff fixed up easily... and hopefully cheaply... before my court date in just under 3 weeks.

The car is throwing codes P0402 and P0420, which I know are EGR and bad cat codes. The EGR one I'll probably let the dealership take care of, but can't I take care of the 420 code with a set of MIL eliminators? When I bought it, the car had an ORH on it with Mac mufflers. In an attempt to quiet it for the neighbors, I had Magnaflows and cats welded in. However, the recent PCM debacle meant the car had to go back to a stock tune, which has caused these codes to throw (whereas before they were simply tuned out).

I'm not sure if the car even has rear 02s. Will the MIL eliminators work just plugged into the front 02s or do they also need a set of rears to be plugged into? Also, what should I look for first in an attempt to correct the EGR problem? Check for carbon buildup, ruptured hoses, and vacuum?

Thanks a bunch guys. You've always helped me over the years with this stuff.