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.
56 Vic, B'Ville 200 MPH Club Member, So Cal.