There's not much more to replace for a "major" tune-up other then plugs
and wires. If it still uses a distributor, maybe a good cap and rotor
could be thrown on, though I thought the 88's were DIS (not sure
though). Definitely change the oil (dirty oil can increase emissions
readings). An air filter if it hasn't been changed recently. As far as
the O2 sensor goes, if it has over 60k miles on the sensor, probably
wouldn't hurt to change it (and with double the HC output, probably a
good suggestion). If you are getting a lot of engine blow-by (which you
can check by looking in the breather tube, one valve cover will have
the PCV valve assembly and the other just a breather tube connected to
the air intake somewhere after the air filter, if that hose shows oil
in it, you can bet you've got blow-by or a bad PCV valve) one trick you
could try is to clean the PCV valve, then put some electrical tape over
it (one piece right over the opening with each end going slightly up
the sides, then one wrap around the outside) then pop it back in
(effectively rendering it inoperative which is illegal). You'll need to
do the same on the breather tube, but don't plug it off all the way,
you'll need to allow it to vent outside the intake track without
looking like it's disconnected. Did I mention that would be illegal?
And if you do disconnect it, by all means reconnect it after the test!
But it may get you through the test. I suppose I'll hear a bunch of
flak for even suggesting that but if you're not intending on keeping
the car much longer and you just need some more time with it...what the
hell. There are much bigger, corporate polluters out there with gov't
issued waivers, and one 2.8L engine on the road for another year won't
break the greenhouse gas bank. And let the bashing begin! :P