i would say no you don't need the gaskets, but, as burdar pointed out, machined surface from the factory didn't use a gasket.
the heatshield is the gasket. if you put another gasket over the heatshield, you run a greater risk of blowing out the gasket
and now the exhaust is leaking there. for the passengers side, the factory had nice new machined surfaces so there was no
leaks without the gasket. but over the years of heat cycles, the manifold can warp a bit. that's when you use the gaskets.
had that problem on the 383 in my Newport. had to have the manifolds machined true. the gaskets would always blow out
after about 3 months.