Ok so I'm about to install a budget Y pipe with a megaflow cat converter and a SP2 system. I just want to make sure the install goes well and I get no CHECK ENGINE LIGHT.

First thing is, the cat converter box is labeled w/O 02, so this means I have to use the 02 sensor thats on my car now, right? Also the box is labeled 97 Nissan. I have a 96, so will this fit my car? From shopping around I notice cat converter being all universal for year 95-01.

The cat will fit fine, but you'll be without your 02 sensor which will throw a CEL. In the '95-'96s, theres a 02 sensor in the cat. '97-'99s have the 02 sensor in either the b-pipe or s-pipe IIRC.

So what will I have to do to keep the CEL off?

Either get an O2 sim, or weld a bung in the new cat and put your existing O2 sensor in there.

Just got Y pipe, cat and SP2 installed today he put the O2 sensor on the pipe after the cat. The 95-96 SP2 already had a bung there. No CEL yet.

Ah perfect then. You should be good to go.