The Lotus head needs the water ways altering to fit the Vauxhall block - reasonably straightforwardmod for a competent welder/machinist. The cam boxes and covers are perfect from a Jensen Healey. The Blydenstein bit for the covers will be harder to get hold of. Parts and set up will be far easier for you than the Vauxhall route and if you have a HC related car technically this is the correct way to go as it is also homologated.