In an effort to save money, Pontiac first eliminated the hole & stud, but left the machined pad/casting in place. They they decided to save a little more money on the casting and cast the heads without the end material to machine a pad.
Their thinking was that the cast iron exhaust manifold was rigid enough to seal on the ports/gaskets. So, the heads work with cast iron exhaust manifolds BUT the problem comes into play when you want to use the factory cast iron Ram Air exhaust manifolds or aftermarket headers which have much thinner steel flanges. Use headers and they will leak, and I suspect the RA manifolds would as well.
bigD provided a great pic of the heads with the machined pad. It can be drilled and tapped by a competent machine shop and an exhaust stud added.
The other style heads do not have that nice pad to work with. I have read that some will drill and tap an exhaust bolt into the corners, but they will break into the water jackets so they needed to be sealed and there is not a lot of material there. Does not sound like a good option in my book.
The other option are a set of "L-brackets" which bolt to the head and provide a stud that allows you to use the end holes on the factory style cast iron Ram Air exhaust manifolds or aftermarket headers to tighten them up. Here is a description and price from one vendor: https://www.opgi.com/gto/G240117/