I believe in a crossover to help with atomization of the fuel mixture. Todays fuel blend does run hotter so I used the “truck” gaskets which restricts the exhaust flow thru the manifold. You can tell it by the stainless attached on the holes. I also purchased a flapper valve replacement spacer with no flapper in it which also helped with heat. You can remove the bimetal spring too. I use Best intake gaskets as many here do.
Back in my early days, 1960, I used tin snips and cut a coffee can lid to make the block offs. Put them on the top of the gaskets, Red high temp RTV will hold them place if you still want the blocked.