I think I know why you thought the car was overheating before, that Engine Coolant Temp sensor has 3 leads on it, one goes to the PCM, the other to your dash gauge, and the third is the ground, I am betting one of the signal wires were intermittently shorting out, so I am betting it was not overheating at all before.
It is still good that you are doing this job, it will save you from the engine failing eventually, those old nylon 6,6 gaskets always fail, it is just a matter of time.
When I replaced my ECT I think I went with a SMP TX-66T at first, but found its readings on the gauge to be off, it was not matching up to what the PCM was seeing, so I had to buy an AC Delco ECT and replace it, that was spot on, AC Delco, or Delphi should be fine,
You can go with the others if money is tight, but there is a chance the readings on the dash will be a bit off, it won't really be off enough to hurt anything though, as long as the PCM see'* the correct temp all is well.
If you get a new ECT that does not have any sealant already in the threads, then you will need a little of this.
I'd get this one if possible.
ACDELCO Part # 213815
Shipped from Rockauto.com it is $18.65 total, and with it you should not need to buy any thread sealant, the threads should already have some on them, I used a tiny bit of plumbers teflon tape as an extra precaution.
The AIRTEX / WELLS Part # 9J8 ECT may work as well, and is a few dollars cheaper, I have not tried that one myself though, I know the AC Delco one works perfectly.
When you replace the sensor make sure to slip that foil looking cover over top of the sensor, that area gets quite hot, which is why the sensor should have had the foil/heat shielding on it.
As for the EGR Stovepipe, I just noticed for some reason most of my pics are gone from that site, I'll have to take the time some day to find the right pics and add them back, without them the thread is incomplete.
That pipe sticking up is the one, I had to lock vice grips on it, and get a little forceful, when it comes out save it, you can use it to put over top the new smaller diameter EGR Stovepipe, and tap it with a hammer to install the new one till it is flush.
NOTE: You should have two stovepipes in that kit, it is easy to tell which one is the right one, only one should fit on the hole correctly.
Let me try to find my pics on the EGR stovepipe.