I recommend not using Cork gaskets on any modern engine, (by modern I mean anything made since the 50's with machined gasket surfaces). They are fine for engines made in the 1920's when trying to seal an as cast surface and will be replaced frequently any way. For sealing machined surfaces, paper or rubberized gaskets are the way to go, in some instances, even a fine bead of silicone alone, no gasket is fine. Any of the other valve cover gaskets will work great, leak free, etc so long as they are not cork and be sure there is absolutely no residual gasket material left on the head or valve covers sealing surfaces. Even a small spec left behind will be prone to leaking oil down the side of the head.
If not using a gasket other than a bead of silicone alone for the L-series valve cover, be sure the valve cover will clear the spinning cam gear/chain as clearance here is already pretty close, especially on heads with cam tower shims.
Hope that helps,
Paul