The least I would do is to get the heavier-bodied high-heat sealer (as normal silicone is a bit runny) and put in into the beads of the stamped steel valley pan gasket. Then scrape them smooth with a gasket scraper to fill in the beads with the silicone. When compressed, that makes the combination into a "printo-seal" gasket where the silcone is compressed when the intake manifold is torqued to specs. If either side (intake manifold or cyl heads) are aluminum, then I would add the 440 6-pk paper gaskets into the mix, too. Let the sealer cure 24hrs.
To me, the spray-on gasket seal is basically gluing the gasket to its mating surfaces. Which also means that disassembly can be more difficult to do. When I used the method I mentioned to re-seal the Edelbrock Torker 383 intake on my '67 Newport, although there was no vac leak per se, it just did not sound "right" to me. After the new valley pan gasket and the added black high-heat sealer, I could tell a difference in how the engine sounded, as it sounded more crisp on off-idle throttle input and such. Obviouisly, a better seal than just the steel gasket could provide on its own.
I devised my use of black high-heat sealer on gaskets on my own, so you won't find it in any book as all gaskets usually are supposed to be installed "dry". It has served me well over the past 30+ years.
Just my experiences,
CBODY
