if all else fails, spend the money and buy the FELPRO set. It is 15 dollars, and comes with the two o-rings, the thermostat gasket, and a couple other gaskets...I forget right now, but I have it in my garage. It is called the 1984-85 Buick GN intake gasket set. You can probably find them easy on federal-mogul site online. Like I said...If you are in the mood for replacing a bunch of things, it is a good kit, but it is 15 bucks. A little steep for just O-rings.
Good Luck!
John