Before the current windshield sealing "silicone" evolved to its current level, butyl tape might have been a desired alternative. Even back then, 3M sold dedicated windshield adhesive for such, but over time, they could lose their grip on the glass and seeps started. Which might explain the silicone you found, which could have been an effort to stop any leaks, back then.
To me, for the butyl tape to work as desired, the body would need to be "perfect" and the glass contours would need to be similarly "perfect". No high spots or shallow spots, as those areas could compromise the seal. If not initially, over time.
By contrast, the 3M windshield sealer is much more forgiving as it comes out in a bead. Which might be what you are terming "the GM way". In reality, any "glue-in" glass does not know any car brand use, just "glue-in" compared to "gasketed".
In many cases, rubber spacers (i.e., travel limiters) are placed at the bottom of the glass area, prior to sealer and glass installation, to ensure the glass stays where it needs to and does not slide down as the sealer cures. Usually about 1/4" square and about 1" long?
Rather than using the 3M Windshield Sealer from a caulking gun, it was possible to purchase something like that in a roll of round sealer. It was thick enough to compress between the glass and have a good seal, much better than flat "tape". Unlike the caulking gun sealer, I suspect it would be more sensitive to shelf life prior to installation, even if stored in a controlled environment. Not unlike how the old "strip caulk" would get stiff with age, although stored in its original box. FWIW
I know this might sound unpopular, BUT I would get a local auto glass company to install the windshield with their materials. You do the clean-out and prep so that all they have to do is wipe down the area and commence with the installation. Most have mobile services (to do onsite work at new car dealerships or "as seen on TV" installations). Two reasons, if they mis-handle the glass and it cracks, it's on them. All of the windshield sealer they use has a lifetime warranty, so if it leaks in the future, it's on them AND they can reseal it for no cost (or at least that's been my experiences). This way, too, they know how much of a bead of sealer to use for best results. To me, these things are worth paying somebody else to do. Your judgment call.
Where did you source the windshield from? Just curious.
Please keep us posted on how things progress, whichever way you decide to go,
CBODY67