Does the intake manifold and distributor have to be removed when changing head gasket on a 1990 Chevy Suburban 350CI?

Yes. To replace the head gasket on a 1990 Chevy Suburban with a 350CI engine, the intake manifold and distributor will need to be removed. Removing the intake manifold will provide access to the cylinder heads while removing the distributor will provide additional clearance allowing easier placement of new head gaskets and help prevent damage during cylinder head reinstallation.