It was traditional for Chevy, Olds, Buick, Cadillac to have no gasket between the cast-iron exhaust manifold and the cast-iron head surface.
Pontiac used gaskets. Go figure.
My '88 C/K service manual makes zero mention of exhaust manifold gaskets for Small-Blocks.
It does say to install the flat washers against the manifold, then the tab washers. Torque the center two bolts to 26 ft/lbs, and the outside bolts to 20 ft/lbs.
Non-cast iron parts will probably need gaskets.
Exhaust manifolds run hotter when there's a gasket between the air-cooled manifold, and the water-cooled head. With no gasket, heat can transfer from manifold to head better.