I recently had this same decision on head gaskets. So, I researched the manufacturer website,
https://www.felpro.com/technical/tecblogs/clean-dry.html for their opinion. They said ,"Fel-Pro gaskets are designed not to need sealers or adhesives. Also; " Use no sealers, adhesives, or other additives to these gaskets." At this site, they also said their head gaskets are designed not to require re-torquing.
I find this hard to believe. I think this technique assumes that both surfaces are in perfectly flat, and clean condition. I also assume that sealant is designed to fill any gap and imperfections. Therefore, I decided to spay the metal side of the gasket with sealer, and not spray the blue side. After giving the engine a good run, I re-torqued the head bolts, where I did notice some bolts did make up more then others.
One thing about the flat-head, the head gaskets are easy to replace, unlike most engines.
Good luck.