That is what I decided to do as well. I placed it around the opening, held it down using the cap to a MAF sensor that I had on hand, then "tacked welded" it in place with four spots of Gorilla Glue super glue. Then a day later, I added four more spots in between the others, for a total of 8 spots.The O ring from the upper manifold that seals the spider is what I used. It took a bit of manipulation but it seals now.
The following are pics with the 4 original super glue spots, each 90 degrees apart:
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I have another of the same O-ring/gasket on order, and I'm going to place that on top of the first one, and secure it in place with more super glue. I think both together will provide a better seal. I'll add some Shin Etsu silicone grease to the O-rings once both are secure in place.
All in all, should provide a pretty good seal.
I searched high and low for just a part number for the original seal, and I do not think GM/ACDelco ever made one available. There's another thread elsewhere on the net that mentions a part number, but that part number is for a completely different part.